Obstetric Procedure–Related Defects : Early Chorionic Villus Sampling, Amniocentesis Needle Injuries, Failed Termination Procedures, Limb Reduction Defects

Genesis

The underlying mechanism for most defects related to problems associated with obstetric procedures is vascular disruption. With chorionic villus sampling (CVS), removal of villi may result in embryonic hypotension, hypoxia, endothelial damage, hemorrhage, and necrosis with tissue loss. Defects are more likely to involve distal structures in the upper body (hands and tongue) than proximal structures or the lower body, with middle digital rays more affected than medial or lateral rays ( Fig. 50-1 ). Following blunt trauma to the placenta, Quintaro et al. noted numerous ecchymoses that might be related to the increased frequency of hemangiomas in CVS-exposed infants. Limb defects caused by vascular disruption have a birth prevalence of 0.22 per 1000, accounting for 34% of all limb reduction defects (which occur with a prevalence rate of 0.69 per 1000). The frequency of terminal transverse limb reduction defects is significantly higher after CVS than in nonexposed pregnancies, with earlier procedures resulting in more severe types of defects and a higher frequency of procedure-related defects. The estimated risk for terminal transverse defects after CVS is estimated to be between 1 : 1000 and 1 : 3000. Therefore it is recommended that CVS only be performed after 10 weeks of gestation. Most experienced operators try to insert the CVS catheter into the chorion frondosum because if the catheter enters the decidua, it can cause hemorrhages. Loss rates after CVS increase with the number of insertions, and inexperienced operators usually require more insertions to obtain adequate samples.

The embryo is normally in a state of partial hypoxia, and because of this state of partial hypoxia, disturbances in the embryo's oxygen supply can more easily lead to a damaging degree of hypoxia. In an experimental setting, mammalian embryos show a surprising degree of resilience to hypoxia, with many organogenic stage embryos able to survive 30-60 minutes of anoxia, but in some embryos this degree of hypoxia causes abnormal development, particularly transverse limb reduction defects. These abnormalities are preceded by hemorrhage, edema, and tissue necrosis. Other parts of the embryo are also susceptible to this hypoxia-induced damage and these include the genital tubercle, the developing nose, the tail, and the central nervous system. Additional frequently observed defects in animal models of prenatal hypoxia include cleft lip, maxillary hypoplasia, and heart defects. Animal studies indicate that hypoxic episodes in the first trimester of human pregnancy could occur by temporary constriction of the uterine arteries. This could be a consequence of exposure to cocaine, misoprostol, or severe shock resulting from failed attempts at pregnancy termination.

Similar exposures have resulted in hypoxia-related malformations in the human, and fetal limb reduction defects have been reported after early hypoxic injury, such as chorionic villus sampling before 66 days' gestation. Failed dilatation and uterine curettage in early pregnancy has been associated fetal oromandibular limb hypogenesis syndrome, which is consistent with this hypothesis concerning the role of hypoxic trauma in inducing fetal structural defects in early pregnancy. Case reports of infants born after failed attempts at dilatation and curettage describe vascular disruption defects such as limb reduction defects and amniotic band–related defects affecting limbs, facial clefts, and the cranium. Failed termination of pregnancy is a relatively rare occurrence, with estimates ranging from 0.02% to 0.07% when termination is undertaken by dilation and curettage or dilation and extraction. Among 2500 unselected patients with arthrogryposis, there were 11 cases of failed termination of pregnancy in which the individuals were subsequently born with arthrogryposis. Infants who survive attempted termination of pregnancy (both surgical and medical) are at increased risk to be born with multiple congenital contractures. Among infants who survived attempted termination of pregnancy and had arthrogryposis, more than half also had intellectual disability. Maternal cocaine use during pregnancy has been associated with congenital contractures, suggesting that vascular compromise may play a role in this type of limb anomaly, and maternal trauma also leads to vascular compromise of the fetus and arthrogryposis. A woman who conceived with an IUD in place had the device removed at 7 weeks' gestation, and her sonogram at 25 weeks' gestation revealed transverse limb reduction of the right forearm. A dichorionic-diamniotic twin was born with hydrocephalus, clubfeet, and hypoplastic toes following myomectomy at 12 weeks' gestation for a 10-cm posterior retroplacental subserous uterine myoma. Severe abdominal trauma at 52 days postconception, caused by blunt trauma to the abdomen, resulted in terminal transverse limb reduction defects and porencephaly.

Needle injuries from amniocentesis have been reported, primarily in the era before ultrasound-guided procedures ( Figs. 50-2 and 50-3 ). Current midtrimester amniocentesis with concurrent ultrasound guidance appears to be associated with a procedure-related rate of excess pregnancy loss of 0.6% and reductions in the incidence of needle punctures and bloody amniotic fluid. Early amniocentesis (at 11 to 12 weeks instead of 15 to 16 weeks) has been implicated as one cause of clubfoot. In the Canadian Early and Mid-Trimester Amniocentesis Trial (CEMAT), the risk of talipes equinovarus was increased from 0.1% with midtrimester amniocentesis to 1.4% with early amniocentesis. Amniotic fluid leakage before 22 weeks was the only significant factor associated with clubfoot, there being a 15% risk with leakage, but only a 1.1% risk without leakage ( Fig. 50-4 ). None of the cases had persistent leakage at 18 to 20 weeks. In some circumstances early amniocentesis might result in a developmental arrest of the foot as it transitions from a normal equinus position at 9 weeks to a neutral position at 12 weeks. The lateral side of the distal tibia grows faster than the medial side, which may result in pressure necrosis of the lateral distal tibia at 11 to 12 weeks.