provides an overview of the prenatal diagnosis of congenital anomalies and termination of pregnancy for fetal anomaly in local deliveries in Oxford during the 10 years 1991-2000 inclusive. Of the 57 258 deliveries (live births, neonatal deaths, stillbirths over 20 weeks, and all pregnancies terminated at any gestation for fetal anomaly), 1208 (2.1%) resulted in a fetus or baby with an abnormality.
Summary chart of prenatal screening and termination of pregnancy for congenital abnormality in Oxford, 1991-2000, inclusive
Of the 57 258 births, 309 (0.5%) were terminated pregnancies because a fetal anomaly had been suspected or diagnosed prenatally. The rate and number of terminations for suspected fetal anomaly increased during the study period, from 129 (129/29 086 (0.4%)) in 1991-5 to 180 (180/28 172 (0.6%)) in 1996-2000. In the same time periods the number of prenatal diagnoses made (with abnormality present at birth) increased from 41% to 46%.7
The investigation that led to the final diagnosis being made was ultrasound scan (that is, structural anomaly, no evidence for chromosome anomaly) in 152 (49%) cases, abnormal karyotype (by chorionic villus sampling, amniocentesis, or fetal blood sampling) in 141 (46%), and molecular testing of DNA in 16 (5%).
shows that the number of terminations of pregnancy in which autopsy was carried out fell from 84% in the first five years to 67% in the second five years.
Number of pregnancies terminated because of fetal anomaly by year (n=309), number of autopsies, and number terminated before 13 weeks' gestation (autopsy not possible before 14 weeks)
gives the final postnatal diagnosis for those fetuses from terminated pregnancies grouped by the body system involved and by lethality as previously described.6
Chromosome anomalies accounted for 141 (46%) of the 309 cases. Neural tube defects and other central nervous system defects were the most common structural defects, accounting for a further 66 (21%) cases. One hundred and thirty three (43%) fetuses were considered to have defects which would have proved lethal, and 44 (14%) defects were possibly lethal. In 132 (43%) the defects were compatible with survival beyond a year.
Number of pregnancies terminated broadly categorised by defect and lethality
In this population during the 10 years of the study there were 1208 fetuses or babies with a malformation. Of these, 601 had a malformation compatible with survival with long term morbidity. If we assume that half of those 44 fetuses with defects classified as possibly lethal (for example, diaphragmatic hernia) did survive (that is, 154 survivors in all), the reduction in prevalence of congenital malformations associated with long term morbidity due to termination of pregnancy would be 26% (that is, 154/601). The true reduction in prevalence would be lower than this because some of the pregnancies would have ended in miscarriage (for example, 43% of Down's syndrome cases diagnosed between the time of chorionic villus sampling and term or 23% between the time of amniocentesis and term8
shows an assessment of the contribution of the autopsy findings to the final diagnosis made for the purpose of counselling after termination of pregnancy for the 132 cases with structural anomalies and no evidence for abnormal karyotype. Autopsy findings led to a refinement of the risk of recurrence (category 3) in 35 (27%) cases. In 11/18 (61%) (category 3b) of those in which the autopsy findings led to an increase in the estimated risk of recurrence this was to a probable one in four risk for subsequent pregnancies. Two of the 132 cases (category 4) could not be classified; termination of pregnancy had been carried out at the parents' request before test results (subsequently normal) had been reported as described previously.6