Late terminations of pregnancy following second trimester amniocentesis.

We sought information from 34 chromosome laboratories in Britain about the frequency during 1982 of late amniocentesis, late reports of prenatal diagnosis results and late resultant terminations of pregnancy. Thirty-one laboratories provided data on a total of 20 840 pregnancies. Gestational age at report was recorded in 14 795 and 510 subsequent terminations of pregnancy were recorded. The data were subdivided into three categories according to the primary indication for amniocentesis: (i) the detection of chromosomal abnormalities, (ii) risk of neural-tube defect, (iii) 'other' reasons. Overall 4.0% of diagnostic amniocenteses were performed at greater than or equal to 21 weeks, 12.7% of reports were made at greater than or equal to 22 weeks gestation, and 13.1% of terminations were performed at greater than or equal to 22 weeks. Late amniocentesis (greater than or equal to 21 weeks) occurred nearly five times more often when the primary indication was the detection of neural tube defects than when it was the detection of chromosomal abnormalities. Approximately two-thirds of 'late' terminations were performed after amniocentesis at greater than or equal to 19 weeks gestation. A total of 3896 (26.3%) of women undergoing prenatal diagnosis had to wait until greater than or equal to 21 weeks gestation before a report was available.