Assisted vaginal delivery in obese women

Although the duration of the second stage of labour is not affected by obesity, and the intrauterine pressure generated by the Valsalva manoeuvre is similar to normal-weight women, maternal obesity is a known risk factor for operative vaginal delivery, which is up to two times more frequent in class III obesity.

The overall success rate of assisted vaginal delivery has been reported to be 86%–91%, but lower rates are found when maternal body mass index exceeds 30 kg/m ² .

Similarly to nonobese patients, the choice of instrument is mainly dependent on operator experience, with vacuum delivery being more likely to fail (OR 1.7; 95% CI 1.3–2.2), to be associated with cephalohaematoma (OR 2.4; 95% CI 1.7–3.4), and retinal haemorrhage (OR 2.0; 95% CI 1.3–3.0), but less likely to be associated with important maternal perineal and vaginal trauma (OR 0.4; 95% CI 0.3–0.5).

A prophylactic dose of intravenous amoxicillin plus clavulanic acid at the time of assisted vaginal delivery was associated, in a single large randomised controlled trial, with a 42% reduction in postpartum infection, and this measure should be considered in obese women, particularly if episiotomy or lacerations have occurred.

The indications for assisted vaginal delivery are the same for obese and nonobese women:

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  Maternal conditions:

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    The inability to push effectively, because of exhaustion or uncoordinated pushing efforts.

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    A medical condition which may be aggravated by the Valsalva manoeuvre (e.g. cardiac or neurologic diseases).

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  Presumed foetal hypoxia:

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    Suspicious or pathologic cardiotocographic tracings.

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  Prolonged or arrested second stage of labour

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    There is no worldwide consensus in these definitions, and the total duration of the second stage of labour (from full dilatation to birth) is frequently confused with the duration of active pushing.

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    The World Health Organisation states that in nulliparous women, birth is usually completed within 3 hours, whereas in subsequent labours it is usually completed within 2 hours. The American College of Obstetricians and Gynaecologists (ACOG) and the Royal College of Obstetricians and Gynaecologists (RCOG) define prolonged second stage when it lasts more than 3 hours in nulliparous women with regional anaesthesia; more than 2 hours in nulliparous women without regional anaesthesia. For multiparous women, these limits are 2 hours with regional anaesthesia, and 1 hour without regional anaesthesia.

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    The International Federation of Obstetrics and Gynaecologists (FIGO) defines a delay in the active second stage when it has lasted 2 hours in nulliparous women and birth is not imminent, 1 hour in multiparous women and birth is not imminent.

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    The recommendation that the second stage of labour should not last more than 3–4 hours is based on strong evidence of a significant increase in maternal and neonatal infection after that time has elapsed.

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    The maximum duration of maternal pushing should take into consideration the frequency and duration of contractions, but most women find it difficult to maintain adequate expulsive efforts for periods greater than 60 minutes.

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    The definition of arrested/protracted labour in the active second stage of labour needs to be adapted to the frequency and duration of uterine contractions, to the mother’s expectations, her physical capabilities, and to the progress of foetal descent.

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    However, action is usually taken if little or no descent is documented by 30 minutes, or if pushing exceeds 60 minutes.

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    Oxytocin augmentation or manual rotation is usually considered at this stage, but an operative delivery should be recommended if little or no progress is observed in the following 30–45 minutes.