Summary A method of estimating fetal weight by ultrasonic measurement of the fetal abdominal circumference is described. Assessment of birth weight predictions on 140 fetuses who were delivered within 48 hours of this measurement showed that the accuracy of predictions varied with the size of the fetus; at a predicted weight of 1 kg, 95 per cent of birth weights fell within 160 g, while at 2 kg, 3 kg and 4 kg the corresponding values were 290 g, 450 g and 590 g respectively. Expressed as a percentage of the predicted weight, confidence limits remained constant throughout the birth weight range. Extrapolation of these data to routine screening of the obstetric population showed that with a single measurement at 32 weeks menstrual age, 87 per cent of babies below the 5th centile would be detected by this method but that the diagnosis rate would fall to 63 per cent at 38 weeks. The false positive diagnosis rate would remain constant between 32 and 38 weeks at just over 1 per cent.

haemoperitoneum was seen and an estimated 400 ml of blood and clots were removed. A transverse uterine rupture of approximately 5 cm was found along the previous caesarean section scar with the fetus protruding through. Significantly, the placenta was normally sited on the posterior wall of the uterus near the fundus. There was also a large left broad ligament haematoma. The fetus and placenta were removed from the uterus and the clots evacuated from the left broad ligament. The transverse uterine tear was repaired. The patient was transfused 3 units of blood.Postoperatively, the patient developed a wound infection and was treated with antibiotics. She was advised against future pregnancies. DiscussionSpontaneous rupture of the uterus early in the second trimester is an exceedingly rare occurrence and is potentially catastrophic. Uterine rupture is typically associated with a past history of uterine trauma such as hysterotomy, myomectomy, cornual resection, classical caesarean section, scar pregnancy, dilatation and curettage or infection. Moriya et al. (1998) reported a case of spontaneous uterine rupture at 28 weeks, secondary to placenta percreta. Endres et al. (2000) reported a case of uterine rupture as early as 15 weeks' gestation after classical caesarean section with placenta percreta. Berghahn et al. (2001) reported rupture of caesarean scar at 23 weeks associated with misoprostol termination of pregnancy. As far as we are aware the case reported here is the first case of spontaneous rupture of lower transverse uterine scar at 16 weeks' gestation without a placenta percreta.The common presenting symptoms of the reported cases associated with placenta percreta were sudden onset of acute abdominal pain and hypotension due to intraperitoneal bleeding. The case described here presented with the symptoms of threatened miscarriage. The sudden increase in the amount of vaginal bleeding and abdominal pain indicated the possibility of uterine rupture. A plausible explanation for the scar rupture in this instance was that some degree of defective healing following the last caesarean section had left a weak scar, which was unable to withstand the force of the uterine activity during the miscarriage. Cervical stenosis is also a predisposing factor in uterine rupture associated with a previous caesarean section, however it would seem unlikely here as there is no history of cervical surgery for CIN or damage due to dilatation. (She had four pregnancies of 37 þ weeks without rupture occurring following evacuation for molar pregnancy suggesting an unscarred cervix). The finding of the placenta attached to the posterior uterine wall near the fundus indicated that placenta percreta was not the cause of the uterine scar rupture. It is worth pointing out that the previous myomectomy scar at the upper part of the uterus remained intact.Caesarean section scar rupture early in the second trimester is an uncommon occurrence. However, clinicians must consider this rare possibility when a patient with previous uterine surgery...

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