Medical Complications of Mothers

Key Principles

• 1.

  Minimize mother–child separation . Whenever possible, a mother should be supported to have her nursing child with her when receiving medical care. Breastfeeding dyads should be welcomed in outpatient offices, and emergency and inpatient settings should implement policies to accommodate nursing dyads. Ideally, these accommodations should include single rooms and bassinets for infants, as well as a space for another adult caregiver to room-in and care for the infant.

• 2.

  Support the lactating patient to drain her breasts every 2 to 3 hours or as often as her child is currently nursing . If the mother is separated from her infant, she should be provided with an electronic breast pump and appropriate supplies. Urgent care centers, emergency departments, surgical centers, and hospitals that care for women of childbearing age should have multiuser breast pumps and supplies available, as well as personnel who are trained to show the lactating patient how to set up the pump to express milk if she is separated from her nursing child.

• 3.

  Select medications with attention to safety profile in lactation . Most medications enter milk in quantities that are unlikely to affect the health of the infant and are therefore safe to use during lactation. The breast functions differently from the placenta, and drug metabolism in lactation differs from drug metabolism in pregnancy; providers should therefore resist the assumption that medication safety in pregnancy can be extrapolated to breastfeeding. Detailed information about specific medications is provided in Chapter 11 . As studies regarding medication in lactation are ongoing, clinicians should consult regularly updated resources such as the National Library of Medicine LactMed database or the Infant Risk Center.

• 4.

  Drain the breasts just before and after procedures . Mothers who have received systemic analgesia or anesthesia can resume breastfeeding once they are awake and alert. Draining the breasts before surgery helps maintain milk production and prevents overfilling, reducing the risk for engorgement and mastitis. After surgery, once the woman is alert and awake, medications have redistributed from the plasma compartment and thus from the milk compartment. For healthy term infants, breastfeeding can resume immediately. A brief delay (6 to 12 hours) may be prudent for infants at high risk for apnea, hypotension, or hypotonia; ⁵ during this time, the mother should be supported to express and discard milk to maintain her supply.

• 5.

  Care plans should address emotional, psychologic, and medical measures to manage the acute illness and support continued lactation . Well-intentioned individuals may advise the patient and her family that it is “too much” to continue to breastfeed in the setting of an acute medical problem. However, abruptly weaning may complicate treatment by precipitating engorgement, mastitis, or breast abscess. Moreover, a hasty decision to interrupt a breastfeeding relationship may lead to long-term regret for the mother. Whenever possible, lactation should be sustained so the mother can participate in a decision regarding whether to continue breastfeeding once she has recovered from the acute phase of her illness.

Key Principles

• 1.

  Address the potential effects of pregnancy complications on breastfeeding as part of routine prenatal care . Obstetric providers should be familiar with the effects of pregnancy complications on infant feeding and should provide tailored anticipatory guidance as part of routine prenatal care.

• 2.

  Communicate maternal risk factors for breastfeeding difficulties to the infant’s care team . Sharing this information will help to facilitate appropriate follow-up of the infant in the early postnatal period.

Hypertensive Disorders of Pregnancy

Hypertensive disorders of pregnancy (HDPs) are associated with fetal growth restriction and indicated preterm birth, both of which can affect early breastfeeding. ⁷ , ⁸ Moreover, women with preeclampsia with severe features are typically treated with intravenous (IV) magnesium for 24 hours after delivery, with side effects of muscle weakness and fatigue that may interfere with rooming-in and caring for a newborn. When postpartum magnesium is planned, consider encouraging a support person to stay with the mother to assist with rooming-in. A published case series describes some of the challenges of establishing breastfeeding among women with HDP, ⁹ suggesting that they may benefit from additional support to establish and sustain breastfeeding.

A research group in India has reported differences in milk composition among mothers with preeclampsia compared with normal controls; ¹⁰ , ¹¹ the clinical significance of this variation is unknown. Women with HDPs are at increased risk for cardiovascular disease in later life, and breastfeeding is associated with reduced cardiovascular risk. ³ In a small prospective study of women with gestational hypertension, maternal blood pressure at 8 months postpartum was lower among those who had lactated compared with those who had never lactated. ¹² Supporting women with hypertensive disorders to breastfeed may improve long-term maternal health.

Antenatal Corticosteroids

When preterm birth is anticipated, antenatal corticosteroids are recommended to reduce the risks for respiratory distress syndrome and other sequelae of prematurity. A 48-hour course of betamethasone 12 mg q24h×2 doses or dexamethasone 6 mg q12h×4 doses reduces the risk for perinatal death, neonatal death, respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, need for mechanical ventilation, and systemic infections in the first 48 hours of life. ¹³ Evidence is limited that antenatal corticosteroids may delay onset of lactogenesis II. In an ovine model, antenatal administration of corticosteroids triggered premature lactogenesis II during pregnancy and disrupted milk production after birth. ¹⁴ In an observational study of women receiving antenatal corticosteroids for anticipated preterm birth, corticosteroid administration was associated with a transient increase in urinary lactose, indicating premature activation of lactogenesis. ¹⁵ Women who delivered at 28 to 34 weeks (N=37) and had received antenatal corticosteroids 3 to 9 days before birth expressed less milk in the first week than women who received antenatal corticosteroids 0 to 2 days before birth. ¹⁶ Women who have recently received antenatal corticosteroids may benefit from additional support to establish lactation.

Operative Birth

Evidence is mixed regarding associations between cesarean birth and breastfeeding outcomes. In a 2012 systematic review of 48 studies enrolling more than 500,000 women in 31 countries, ¹⁷ cesarean birth was associated with lower breastfeeding initiation than vaginal birth (odds ratio [OR] 0.57, 95% confidence interval [CI] 0.50 to 0.64). Among studies that distinguished unlabored from in-labor cesarean birth, only unlabored cesarean was associated with lower initiation compared with vaginal birth (unlabored: OR 0.83, 95% CI 0.80 to 0.86; in labor: OR 1.00, 95% CI 0.97 to 1.04). Among women who initiated breastfeeding, cesarean birth was not associated with a difference in any breastfeeding at 6 months (OR 0.95, 95% CI 0.89 to 1.01). A subsequent systematic review of cesarean birth and breastfeeding in China ¹⁸ found considerably lower rates of exclusive breastfeeding in the early postpartum period (OR 0.53, 95% CI 0.41 to 0.68) and of any breastfeeding at 4 months (OR 0.61, 95% CI 0.53 to 0.71).

Few studies have tested strategies for enabling women to breastfeed after cesarean birth. Promising strategies include targeted assistance ¹⁹ and early skin-to-skin contact in the operating room. ²⁰ A small randomized controlled trial (RCT) found that advising women who birthed by cesarean to pump after at-breast feeding in the first 72 hours postpartum did not improve milk transfer and reduced median duration of breastfeeding among primiparous women (4.2 vs. 9.7 months, p =0.18); routine mechanical expression after cesarean is thus not recommended.

Few studies have evaluated the relationship between operative vaginal delivery and breastfeeding outcomes. ²¹ , ²² , ²³ In a study of 370 births in a Denmark hospital in 1986, infants born by vacuum extraction were more likely to be supplemented with formula than spontaneously born infants, and mothers reported that their milk came in later, but breastfeeding rates were similar through 6 months of life. A 2003 study of 393 women with operative births in the second stage at two teaching hospitals in Bristol, United Kingdom in 1999 to 2000 found similar breastfeeding outcomes among women with cesarean versus operative vaginal births. However, compared with women with a failed instrumental birth, women who underwent cesarean without a trial of instrumental birth were more likely to be breastfeeding at 1 year postpartum (39.8 vs. 29.1%, adjusted OR [aOR] 1.59, 95% CI 1.09 to 2.32). In a Hong Kong study of 8327 births in 1997, instrumental vaginal birth was associated with higher odds of stopped breastfeeding before 1 month compared with spontaneous vaginal birth (OR 1.32, 95% CI 1.04 to 1.68). In a recent RCT ²⁴ of prophylactic antibiotics after operative vaginal birth in which 89% underwent episiotomy, 51% of women were breastfeeding at 6 weeks. Treatment was associated with lower rates of women reporting “perineum ever too painful or uncomfortable to feed baby” (11 vs. 17%, p < 0.001). The rate of perineal discomfort in both groups suggests that women with significant perineal lacerations may benefit from help feeding while side-lying.

Intrapartum Analgesia and Anesthesia

The association between intrapartum pain management and breastfeeding outcomes is complicated by multiple factors, including maternal coping and pain tolerance, length and difficulty of labor, and maternal intention to breastfeed. ²⁵ Moreover, RCTs are difficult to conduct given personal preferences among laboring women regarding pain management. A 2016 systematic review identified 23 studies that evaluated epidural anesthesia and breastfeeding outcome: 12 found negative associations, 10 showed no association, and one showed a positive association. ²⁶ The Academy of Breastfeeding Medicine (ABM) recommends that particular care be taken to provide mothers who have received neuraxial anesthesia with good breastfeeding support and close postpartum follow-up. ²⁵

Parenteral opioids cross the placenta and can depress newborn respiration and neurobehavior. Long-acting opioids with active metabolites, such as meperidine/pethidine, should be avoided. ²⁵ Data on nitric oxide for labor analgesia and breastfeeding outcomes are limited, but the half-life of nitric oxide in the neonate is 3 minutes and extant evidence is reassuring. ²⁷

Postpartum Hemorrhage

Postpartum hemorrhage is associated with difficulty initiating and sustaining lactation. In a population-based study in Australia of women with a discharge diagnosis code for postpartum hemorrhage (N=39,787), transfusion was associated with lower rates of any breastfeeding (adjusted relative risk [aRR] 0.91, 99% CI 0.92 to 0.95) and of exclusive breastfeeding (aRR 0.93, 99% CI 0.91 to 0.95) at hospital discharge. ²⁸ Among transfused women, there was a dose-dependent association between lower pretransfusion hemoglobin and lower breastfeeding rates at discharge. ²⁹ A multicenter longitudinal study of women with a postpartum hemorrhage of greater than 1500 mL found lower rates of full breastfeeding in the first week among women with cesarean or assisted vaginal births or whose first suckling was delayed for longer than 5 hours. Full breastfeeding rates were 63% at 1 week, 58% at 2 months and 45% at 4 months postpartum. In qualitative analyses of women who experienced hemorrhage, the three key themes were (1) difficulty initiating or sustaining breastfeeding, (2) need for education and support, and (3) emotional sequelae. For some women, the trauma of a severe postpartum hemorrhage was compounded by breastfeeding difficulties. One participant wrote, “not being ‘mobile’ meant the only thing I can do for my new son was to breastfeed, and when that fell over, upset and feelings of uselessness set in. . . . I did begin to develop postnatal depression when I was unable to continue breastfeeding, which I found very difficult and disappointing.” ³⁰

Sheehan Syndrome

Hypotension in the setting of postpartum hemorrhage can cause Sheehan syndrome, an infarction of the anterior pituitary gland, resulting in loss of pituitary function. ³¹ The expansion of the pituitary because of proliferation of lactotrophs during pregnancy is thought to make it vulnerable to hypoperfusion. Sheehan syndrome is more common in low-resource settings in which women do not have access to modern obstetric care. Along with failure of lactation, acute Sheehan syndrome may manifest with severe hypopituitarism with symptoms of hypotension, hypoglycemia, hyponatremia, shock, headache, visual disturbances, or loss of consciousness. Damage to the posterior pituitary can cause diabetes insipidus. Loss of adrenocorticotropin hormone (ACTH) can be fatal if not treated with glucocorticoids to restore adrenal function.

In other cases, patients may present with a chronic-onset panhypopituitarism or partial hypopituitarism years after the inciting hemorrhage. Symptoms include somnolence, premature aging, mental apathy, physical weakness, nausea, anorexia, anemia, and marked cold sensitivity. Most patients also report a history of being unable to produce milk, with postpartum breast involution and prolonged amenorrhea. This gradual loss of pituitary function may be mediated by pituitary autoantibodies that develop after postpartum pituitary necrosis. In a published case report, a 54-year-old woman presented with a syncopal episode and was found to be in adrenal crisis with panhypopituitarism. Her medical history was significant for postpartum hemorrhage at the birth of her son 19 years ago. Magnetic resonance imaging (MRI) revealed an empty pituitary sella, confirming the diagnosis of Sheehan syndrome. ³²

The three essential diagnostic criteria for Sheehan are (1) typical history of severe postpartum uterine bleeding, particularly at last delivery; (2) at least one pituitary hormone deficiency; and (3) partial or complete empty sella on MRI or computed tomography (CT) in the chronic phase. ³¹ Suggesting criteria include (1) severe hypotension/shock at index delivery, (2) postpartum amenorrhea, and (3) postpartum agalactia. Laboratory workup includes assessment of pituitary hormones. Findings of hypopituitarism include low serum cortisol with a low or normal ACTH level; low free triiodothyronine (T ₃ ) and free thyroxine (T ₄ ) with low thyroid-stimulating hormone (TSH), low estradiol with a low or normal follicle-stimulating hormone (FSH), and luteinizing hormone (LH) level; low insulin-like growth factor levels; and low baseline prolactin in the setting of agalactia. An ACTH stimulation test may be normal in the early postpartum period before the adrenal cortex has atrophied.

Intensive Care Unit Admission

In surgical and medical intensive care units, mothers are typically separated from their infants and may be intubated and paralyzed. Regular stimulation and draining of the breasts is important to establish lactation, because the critically ill mother may not be able to express milk herself. Clinical staff should assist the critically ill patient to express milk so that once she is awake and alert, she can make a decision about whether to breastfeed. ³³

Retained Placenta

Withdrawal of placental hormones after birth facilitates onset of lactogenesis II, and retained placenta has been described as a cause of delayed lactogenesis. Neifert et al. ³⁴ reported three cases of failed lactogenesis that resolved after emergency curettage with recovery of placental fragments in the setting of delayed postpartum hemorrhage. A 2001 case report describes a woman with two pregnancies and one birth (G2P1) who had previously breastfed without difficulty. ³⁵ At day 9 postpartum, she was producing minimal colostrum. On day 18, her beta human chorionic gonadotropin (hCG) was 225 mIU/mL and she was diagnosed by MRI to have placenta increta. After treatment with methotrexate and an episode of heavy vaginal bleeding, she experienced engorgement. Her hCG at that time was less than 5 mIU/mL. After a period of expressing and discarding her milk to avoid infant exposure to methotrexate, she fully breastfed her infant. Failure of lactation in the setting of abdominal pregnancy with placenta left in situ also has been described, although the authors acknowledge that multiple factors may have contributed. ³⁶ These cases support evaluation for retained placenta in the setting of failed lactogenesis.

Hyperreactio Luteinalis

Hyperreactio luteinalis (HL) manifests with massive cystic enlargement of the ovaries in response to abnormally elevated hCG or ovarian hypersensitivity. HL is more common in the setting of multiple gestations and gestational trophoblastic disease. Theca lutein cysts may be detected incidentally on antenatal ultrasound or at cesarean, or patients may present with abdominal pain or torsion. Women with HL may also present with elevated testosterone or symptoms of virilization. In a literature review, authors identified 52 reports describing 58 pregnancies affected by HL, among whom 30% reported symptoms of maternal virilization. ³⁷

It has been proposed that elevated testosterone levels after birth may delay onset of lactation. Two case series have reported on lactation outcomes in a total of four women, ³⁸ , ³⁹ with onset of lactogenesis as serum testosterone fell. In the reported cases, after an initial period of supplementation, three of the four women were able to exclusively breastfeed. Serum testosterone may be helpful in evaluating delayed onset of lactation in women with ovarian cysts.

Postpartum Emergency Visits and Readmissions

In the United States, approximately 2 in 100 women are readmitted within 6 weeks postpartum; the most common indications for readmission are hypertensive disorders, wound infection or breakdown, psychiatric disease, uterine infection, and gallbladder disease. ⁴⁰ Among publicly insured women in the United States, one in four had at least one emergency room visit in the 6 months postpartum. ⁴¹ To ensure that breastfeeding is not disrupted, acute care settings should assess whether patients are lactating and accommodate mother–infant contact and/or access to a breast pump, as detailed earlier in the discussion of acute care.

Key Principles

Maternal health conditions affect breastfeeding through multiple mechanisms ( Box 15.1 ), as follows:

• 1.

  Risk for congenital anomalies . Fetal anomalies complicate about 3% of live births. Craniofacial anomalies, such as cleft lip and palate, directly interfere with at-breast feeding (see Chapter 13 ); other anomalies, such as congenital heart defects, may require newborn intensive care or surgical repair in the early days of life, complicating breastfeeding initiation. Both maternal chronic diseases and medications are associated with an increased risk for birth defects.

• 2.

  Fetal growth and risk for preterm delivery . Maternal health conditions can affect the risk for pregnancy complications, fetal growth restriction, and preterm birth. Cardiometabolic diseases, including obesity, hypertension, and diabetes, confer an increased risk for preeclampsia, which may result in indicated preterm or early term birth. As discussed in Chapter 14 , prematurity complicates establishment of breastfeeding, particularly if the mother and infant are separated and the infant is admitted to the neonatal intensive care unit (NICU).

• 3.

  Transition to extrauterine life and initiation of lactation . Maternal disease can have impact on neonatal physiology through effects on placental growth and development and through transplacental transfer of maternal medications, glucose, antibodies, and other bioactive molecules affecting the newborn’s transition to extrauterine life. Maternal health conditions can also disrupt the endocrinology of breast development and milk synthesis, resulting in delay of lactogenesis II and reduced or absent milk production.

• 4.

  Environment, health, and milk composition . Anthropologic studies have found that human milk composition varies depending on characteristics of the maternal environment, and this variation reflects protective adaptations that improve the fitness of the mother–infant dyad. ⁴² , ⁴³ Emerging studies have characterized the “omics” of human milk composition and explored variations in milk macronutrients, oligosaccharides, hormones, and microbiome.

• 5.

  Maternal medications, milk synthesis, and the breastfed infant . When considering the impact of medical management of maternal disease on breastfeeding, it is critical to understand that the pharmacology of medication exposure during pregnancy is different from the pharmacology of medication exposure during lactation. During pregnancy, agents in maternal circulation are transferred via the placenta to the fetal circulation by diffusion or active transport. These medications may affect early breastfeeding through their effects on fetal development and transition to extrauterine life. During breastfeeding, agents may or may not transfer into milk, and any agents ingested by the infant may be digested in the infant gut and may or may not be enterally absorbed. Maternal medications can also affect milk production through effects on blood flow to the breast and through hormonal signals that regulate milk production. Medications and herbal preparations during breastfeeding are discussed in detail in Chapter 11 , and the relationship between lactation physiology and reproductive hormones is discussed in Chapter 3 .

• 6.

  Physiologic demands of breastfeeding and maternal health . Both pregnancy and lactation change maternal physiology, and these endocrine and immunologic changes may aggravate or alleviate maternal diseases. Pregnancy downregulates cellular immunity to support tolerance of the fetal allograft, and some autoimmune diseases improve during pregnancy, only to relapse in the postpartum period. Studies of breastfeeding and relapse rates are potentially confounded by maternal disease severity, in that women with more significant disease before pregnancy may be less likely to initiate breastfeeding, because of concerns such as maternal fatigue or infant exposure to maternal medications. The maternal endocrine effects of exclusive breastfeeding, including elevated prolactin and reduced estrogen and progesterone, are distinct from mixed feeding ⁴⁴ and may have different effects on maternal disease course.

  Lactation substantially affects maternal metabolism. Mothers of exclusively breastfeeding infants produce about 700 to 800 g of milk a day, at an energy cost of 597 to 716 kcal (2.5 to 3 MJ) per day ( Table 15.1 ). ⁴⁵ This metabolic load may be mobilized from fat stores or from dietary intake, depending on the local availability of nutrition to the mother. This significant metabolic load affects and is affected by maternal diseases. Women with health conditions that affect nutrient absorption may have difficulty sustaining sufficient caloric intake and may benefit from consultation with a nutritionist.

  Table 15.1

  Energy Cost of Milk Production for Exclusive and Partial Breastfeeding ^a

  From Butte NF, King JC. Energy requirements during pregnancy and lactation. Public Health Nutr . 2005;8(7A):1010–1027.

  Postpartum Period (mo)	0–2	3–5	6–8	9–11	12–23
  	Energy cost of milk production (MJ day −1 )
  Exclusive breastfeeding
  Industrialized countries	2.49	2.75	2.81	3.15
  Developing countries	2.50	2.74	2.72
  Partial breastfeeding
  Industrialized countries	2.24	2.40	2.07	1.53	1.57
  Developing countries	2.16	2.32	2.31	2.16	1.92

  a Energy cost of lactation based on milk production rates from Brown K, Dewey KG, Allen L. Complementary Feeding of Young Children in Developing Countries: a Review of Current Scientific Knowledge . Geneva: World Health Organization, 1998., milk energy density of 2.8 kJg ⁻¹ and energetic efficiency of milk synthesis of 0.80.

  In addition, lactation suppresses the hypothalamic-pituitary-ovarian axis. Prolactin suppresses gonadotropin-releasing hormone (GnRH) and delays return of menses, resulting in lower circulating estrogen and progesterone levels, as discussed in detail in Chapter 3 . During lactation, the hypothalamic–pituitary–adrenal (HPA) axis is also suppressed; cortisol levels decrease during breastfeeding episodes, ⁴⁶ , ⁴⁷ , ⁴⁸ and the HPA response to physical stress is diminished in breastfeeding women compared with that in bottle-feeding women. ⁴⁹ Breastfeeding mothers also demonstrate increased parasympathetic and decreased sympathetic activation, compared with bottle-feeding mothers. ⁴⁹ , ⁵⁰ , ⁵¹ , ⁵² These changes, in turn, may have an impact on maternal chronic disease trajectories.

  Prolactin is secreted from the anterior pituitary and stimulates milk production. Downregulation of dopamine stimulates pulsatile secretion of pituitary prolactin; other triggers for pituitary prolactin include thyrotropin-releasing hormone, estradiol, oxytocin, vasopressin, ghrelin, endogenous opioids, serotonin, and angiotensin II. Prolactin is also produced in the breast, the brain, the decidua, and multiple cell lines, including lymphocytes, skin fibroblasts, and adipose cells. ⁵³ Alternative splicing of prolactin mRNA as well as posttranslational modifications result in multiple prolactin isoforms, which likely mediate its pleiotropic effects. Both B cells and T cells express prolactin and prolactin receptors, such that prolactin participates in both endocrine and paracrine/autocrine regulation of immune function. ⁵⁴ Higher levels of prolactin are reported in patients with autoimmune diseases ⁵⁵ , ⁵⁶ (discussed in the later section on breastfeeding and autoimmune disease). Prolactin is also implicated in pancreatic beta cell expansion during pregnancy, ⁵⁷ and higher prolactin levels during pregnancy are associated with improved beta cell function at 3 months postpartum. ⁵⁸

• 7.

  Practical demands of breastfeeding . Exclusive breastfeeding is demanding. In a time use study, Smith and Forrester ⁵⁹ found that lactating mothers spent about 8.5 hours more per week feeding and caring for infants than nonlactating mothers. ⁵⁹ This investment of time may be difficult to sustain for women with chronic health conditions. Moreover, nighttime feedings may be especially challenging for women for whom sleep is a medical need, such as women with epilepsy ⁶⁰ or bipolar disorder. ⁶¹ These medically necessary periods of rest can result in breast overfilling and engorgement, and strategies are needed to support draining the breasts with minimal disruption of maternal sleep. The mother and her provider should work together to develop a strategy for both supporting her health and enabling her to breastfeed. ⁶² Options to consider include the following:

  • Before going to sleep, feed and/or express milk to prolong the time until the breasts feel uncomfortably full.

  • Express milk and sleep through a nighttime feeding while another caregiver looks after the baby.

  • Have another adult caregiver assume responsibility for all aspects of infant care except for feeding. When the infant cues to feed, the other caregiver can bring the baby to the mother, gently wake her, and assist the baby to nurse while she is side-lying, so that she can continue to rest. When the feeding ends, the other caregiver is responsible for changing, settling, and soothing the baby while the mother goes back to sleep.

  • Keep a pump and a cooler at the bedside so that if the mother wakes and feels uncomfortably full, she can express milk to comfort and resume sleep with minimal disruption.

  For some women, getting sufficient sleep to prevent complications such as mania, postpartum psychosis, or recurrent seizures may affect milk production. It is imperative for breastfeeding medicine providers to support the whole mother–baby dyad and work with the family to craft a sustainable strategy that takes into account the importance of both human milk and maternal well-being.

• 8.

  Lactation duration, intensity, and long-term maternal health . In observational studies, longer duration and greater intensity of breastfeeding are associated with substantial differences in women’s health across the life span, as detailed in Chapter 6 . These findings suggest that enabling women to breastfeed may improve long-term health for women. These population-level differences likely reflect both the effects of breastfeeding on maternal physiology and the extent to which being able to sustain breastfeeding is a marker for maternal health and well-being. ⁶³

Illustrating the Intersection Between Lactation and Maternal Chronic Conditions: Diabetes

Diabetes is one of the most common chronic diseases among childbearing women, and its multiple effects illustrate the interplay between maternal disease and breastfeeding. About 1% to 2% of pregnancies are complicated by pregestational diabetes, ⁶⁴ and an additional 6% develop gestational diabetes, defined as glucose intolerance first diagnosed during pregnancy. ⁶⁵ Here, we use diabetes to illustrate the links between breastfeeding and maternal chronic health conditions.

Effects of Maternal Conditions on Breastfeeding

Effects of Medications to Treat Diabetes on Milk Supply

Given the potential role of insulin resistance in low milk production, metformin has been proposed as a galactogogue. Metformin is a derivative of guanidine, one of the metabolically active compounds in Galega officinalis , or goat’s rue. ⁸⁴ Goat’s rue is so-named because it increases milk production in goats. In an RCT of metformin during pregnancy for women with polycystic ovary syndrome (PCOS), women randomized to metformin had a slightly longer duration of exclusive breastfeeding (4.5 vs. 3.9 months, p =0.08). ⁸⁵ A pilot study (N=15) of initiating postpartum metformin for women with insulin resistance and low milk supply found a small increase in milk produced among women in the metformin arm, and a decrease in women in the placebo arm (median change [interquartile range], + 22 [–5 to + 54] mL/24 h versus –58 [–83 to –1] mL/24 h, metformin versus placebo + noncompleters, Wilcoxon rank-sum p value=0.07). These results support the hypothesis that modulating insulin resistance may improve milk supply; however, the increase in production was modest. An ongoing clinical trial of insulin versus metformin + insulin to treat overt diabetes in pregnancy [NCT02932475] is collecting data on breastfeeding outcomes, which may inform future treatment recommendations.

The Effects of Lactation on Maternal Diabetes Management

The energy load of lactation modifies metabolic requirements for women with diabetes. Among a small sample of postpartum women with type 1 diabetes who underwent continuous glucose monitoring, breastfeeding women (N=8) had slightly higher carbohydrate intake, but similar insulin requirements, to formula-feeding women (N=8). In the 3 hours after suckling, glucose levels gradually dropped, resulting in hypoglycemia (glucose < 4 mmol/L or 72 mg/dL) in 9.9% of episodes at 2 hours and 13.5% of episodes at 3 hours after suckling. Overall, there was no difference in frequency of hypoglycemia among breastfeeding versus formula-feeding women in this small sample. The authors speculate that women who were breastfeeding increased their carbohydrate intake to compensate for the demands of breastfeeding.

For women with gestational diabetes, breastfeeding during the postpartum oral glucose tolerance test (OGTT) is associated with differences in postload results. In a prospective cohort study of women with GDM who were breastfeeding at their 75-g oral OGTT visit, fasting glucose levels were similar, but 2-hour insulin levels and postload glucose levels were lower (glucose mean adjusted difference: −6.2 mg/dL, 95% CI −11.5 to −1.0), and insulin sensitivity was higher, for women who breastfed during the OGTT than for women who did not in models adjusted for race, parity, age, number of abnormal results for 3-hour prenatal OGTT, amount of formula supplementation (oz/24 h), and fasting period (hours). ⁸⁶

Thyroid Disorders

During pregnancy, thyroid binding globulin (TBG) and total T ₄ levels increase dramatically, peaking by 16 weeks of pregnancy. ⁸⁸ After delivery, estrogen, TBG, and total T ₄ levels decline. ⁸⁹ Data are limited on normal thyroid levels in lactation; in a small sample of exclusively breastfeeding women (N=28), free T ₄ levels fell from 2 to 8 weeks postpartum (median values, CI 5% to 95%; 2 weeks: T ₄ =0.97 ng/dL, 0.79 to 1.32; 8 weeks: T ₄ =0.90 ng/dL, 0.67 to 1.18, [paired t test, 2 versus 8 weeks, probability <0.001]). ⁹⁰

Parathyroid Disorders

Effects of Lactation on Calcium Metabolism

Calcium homeostasis changes during pregnancy and lactation to support the needs of the fetus and neonate. ⁹² , ⁹³ During pregnancy, intestinal absorption of calcium doubles, mediated by increased levels of 1,25 dihydroxyvitamin D (calcitriol), prolactin, human placental lactogen, and other factors. By term, the fetus accrues 30 g of calcium, more than 80% of which is transferred in the third trimester. During lactation, women transfer 210 mg/day into breast milk for the neonate ( Fig. 15.2 ). This calcium is primarily obtained from resorption of maternal bone stores, caused by low levels of estrogen and by parathyroid-related peptide (PTHrP) produced in the mammary gland. Indeed, the lactating breast has been described as an accessory parathyroid. ⁹² , ⁹³ Increased calcitonin levels in the first 6 weeks of lactation counter the effects of PTHrP, preventing excessive maternal bone loss. This transfer of calcium results in a 5% to 10% loss of bone density in the first 2 to 6 months of breastfeeding. Although one longitudinal study found lasting changes in maternal bone microarchitecture, ⁹⁴ most studies have found that maternal bone density returns within 6 to 12 months of weaning. ⁹⁵ Of note, a systematic review of 11 studies including 101,726 women found no association between breastfeeding and postmenopausal fracture risk. ³

Calcium supplementation beyond the recommended daily allowance of 1.2 g/day of calcium is not recommended during pregnancy or lactation, and dietary supplements do not change milk composition or affect maternal bone metabolism. For women with low dietary calcium intake (<600 mg/day), supplementation is recommended by the World Health Organization to reduce risk for HDPs and preterm birth. ⁹⁶ However, the effects of supplementation on bone health are unclear. In a postnatal follow-up study of Gambian women with low dietary calcium intake (<350 mg/day), those randomized to supplementation with 1500 mg calcium per day had lower bone mass through 12 months postpartum. These differences persisted after weaning. ⁹⁷ The authors propose that calcium supplementation altered women’s ability to conserve calcium in the setting of a low-calcium diet. ⁹⁸