Midtrimester amniocentesis: is it safe? A single centre controlled prospective study of 517 consecutive amniocenteses.

The outcome of pregnancy following amniocentesis was studied prospectively in 517 consecutive patients undergoing amniocentesis in a single centre. The outcome in 289 of these pregnancies was compared with that in 289 control patients strictly matched for social class, age and parity. There were no significant differences in fetal loss, perinatal mortality or vaginal bleeding between the amniocentesis and control groups. There were significantly more congenital abnormalities in the amniocentesis group (P less than 0.01). These appear to be associated with the amniocentesis procedure and not with the occurrence of raised maternal serum alpha-fetoprotein levels. Although there was an increased risk of preterm delivery (P less than 0.02) there was no significant difference in the distribution of birthweights by centiles for gestational age between amniocentesis and control groups. There was a significant association between intrauterine growth retardation and raised serum alpha-fetoprotein (P less than 0.005). It is concluded that where the indications are strong, amniocentesis continues to be justified.