Serum markers for Down's syndrome in women who have had in vitro fertilisation: implications for antenatal screening

To examine the Down's syndrome screening positive rate among in vitro ferti lisation (IVF) pregnancies, we measured second trimester serum marker level s in singleton IVF pregnancies (cases) and in five non-IVF pregnancies (con trols) matched to each case for gestational age, age of mother, and duratio n of storage of the serum sample. There were 151 IVF pregnancies in which a lpha fetoprotein, unconjugated oestriol (uE(3)), free beta-human chorionic gonadotrophin (hCG) and total hCG were measured, 104 IVF pregnancies in whi ch free alpha-hCG was measured, and 39 IVF pregnancies in which inhibin A w as measured. Median uE(3) levels were 6% lower (P = 0.003), median free bet a-hCG 9% higher (P = 0.024), and median total hCG 14% higher (P = 0.026) in IVF pregnancies compared with controls. The screen positive rate in the IV F pregnancies (28%) was about twice as high as that in controls (17%). High hCG levels may be explained by progesterone remaining high in IVF pregnanc ies. The low uE(3) levels remain unexplained. In Down's syndrome screening in IVF pregnancies hCG and uE(3) values should be adjusted to avoid the hig h screen positive rate.