Most estimated fetal weight formulas have been derived and tested with larger fetuses, yet accuracy in predicting birth weight is more critical at the limit of viability. Complete data from 142 pregnancies in which delivery took place within 7 days of an ultrasonographic examination were used to create an appropriate formula for fetuses less than 1000 g and compare it with 10 currently available formulas. Our formula (In [BW] = 0.66 x 1n [HC] + 1.04 x 1n [AC] + 0.985 x 1n [FL]) was significantly more accurate than all other formulas and also performed better on a prospective cohort of 27 fetuses with estimated fetal weight less than 1000 g. Of the existing formulas, the Hadlock formula (using head circumference, abdominal circumference, femur length) was the most accurate, being significantly more accurate than all but the Woo formula with all but the Woo formula.

A combination of maternal age, NT and maternal serum biochemistry gives a high detection rate for both trisomy 21 and other chromosomal abnormalities. Down syndrome screening using either maternal age alone or age in combination with first trimester biochemistry conferred screen positive rates significantly higher than when combined with NT.

Before chorionic villus sampling at 10–13 weeks' gestation, 453 women had the crown–rump length and nuchal translucency (NT) measured with transabdominal ultrasound. There were 19 aneuploid pregnancies (ten cases of trisomy 21, six of trisomy 18, one of 47+marker, one 47,%, and one 45,X mosaic). Average NT was 1·7 mm (range 0–5 mm), correlating with the crown–rump length, but not maternal age. A static cut‐off of 2·5 mm gave a false‐positive rate of 1·3 per cent for crown–rump length between 30 and 35 mm, rising to 13 per cent in fetuses with a crown–rump length between 50 and 65 mm. This gave an overall false‐positive rate of 5·5 per cent for a detection rate of 30 per cent for trisomy 21. Applying a dynamic action limit (95th centile), the false‐positive rate remained at 5 per cent irrespective of the crown–rump length, detecting 30 per cent of trisomy 21 and 36·8 per cent of all aneuploidies. Raising the action limit to the 97·5th centile halved the false‐positive rate (2·5 per cent), with no change in trisomy 21 detection and only a slight decrease in aneuploidy detection (31·6 per cent). Aneuploid fetuses showed normal first‐trimester growth. NT increases with gestational age, making a dynamic action limit necessary to decrease the false‐positive rate, while maintaining aneuploidy detection rates. Aneuploidy does not cause significant first‐trimester growth retardation, enabling normal ranges for NT with crown–rump length to apply.

We conducted a retrospective cohort study to assess the risk of amniocentesis in twin pregnancy for adverse outcomes. The study base consisted of women who had an amniocentesis performed during twin pregnancy and a comparison representative sample of women who carried a twin pregnancy, but did not have invasive prenatal diagnosis. The 227 women in each of the exposed and non-exposed groups were residents of the state of New South Wales, Australia, over the period 1980-92, and were matched on maternal age and period of the infant's birth. Nearly 10% of twin pregnancies among the women having an amniocentesis were affected by a stillbirth, and the stillbirth rate among exposed fetuses (5.3%) was nearly twice as high as among non-exposed fetuses (3.1%). After adjustment for confounding and excluding abnormalities, there was a non-significant elevated relative risk of stillbirth after exposure to amniocentesis. The analysis by type of amniocentesis (with and without methylene blue dye) was limited by small numbers, but the burden of risk was primarily among women who had dye exposure during amniocentesis (relative risk = 3.64, 95% confidence interval = 1.15, 11.48). This increase remained after adjusting for confounding, although the confidence interval was wide. In conclusion, we were unable to establish with certainty whether an increased risk of stillbirth could be ruled out among women who had any type of amniocentesis in twin pregnancy.

Congenital bronchopulmonary malformations detectable on prenatal ultrasound include cystic adenomatoid malformation (CAM), lobar sequestration, and upper airway atresia. We describe three fetuses with prenatally detected intrathoracic lesions in which the associated pulmonary hyperechogenicity disappeared before delivery. In the first case of pulmonary sequestration, the infant was asymptomatic after birth. However, in a case of CAM and another with laryngeal atresia, respiratory distress developed after delivery, despite recent scans showing apparently normal lung fields. This experience suggests that ultrasonic resolution of hyperechogenic lung lesions in utero does not necessarily indicate resolution of the underlying pathology.