Risk factors associated with the development of shoulder dystocia during labour include:

Large Foetus

Small Maternal Pelvis

      Pelvimetry involves estimating the dimensions of a gynecoid (or female) pelvis. The normal pelvic inlet has an AP (antero-posterior) diameter of 11cm and a transverse diameter of 13.5cm; the mid pelvis has an AP diameter of 12cm and a transverse diameter of 12cm; and the pelvic outlet has an AP diameter of 13.5cm and a transverse diameter of 11cm. If for any reason the dimensions of a female pelvis fall below the above, the pelvis becomes less than ideal for childbirth and there is an increased risk of shoulder dystocia occurring during delivery even in the absence of macrosomia.

Post Maturity

      It is necessary to distinguish between prolonged pregnancy and post maturity. Prolonged pregnancy is defined as pregnancy exceeding 42 completed weeks of gestation or pregnancy exceeding 14 days from the normal length of 280 days (note that the first day of a pregnancy is the first day of the last normal menstrual period). Post maturity is a syndrome associated with meconium stained liquor, oligohydramnios and observational loss of subcutaneous fat with dry, cracked skin of the baby following delivery. The syndrome of post maturity can occur in a pregnancy less than 42 completed weeks of gestation and diagnosis is best made after delivery.

      Post maturity is a factor that has been known to be associated with shoulder dystocia.

Previous Shoulder Dystocia

      There is a risk of recurrence of shoulder dystocia in subsequent pregnancies although definite figures are not available.

Prolonged Second Stage Of Labour

      Labour occurs in three stages - stage one begins with painful, regular and progressive uterine contractions and ends with cervical effacement and dilation up to 10cm; stage two ends with the delivery of the foetus and stage three ends with delivery of the placenta.

      Failure of the foetal head to descend during the second stage of labour; and a lengthy second stage of labour are associated with shoulder dystocia.

Assisted Vaginal Delivery

      Shoulder dystocia has been found to be more common in instrumental deliveries than in spontaneous vaginal deliveries.


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