To establish gestational age-specific and body weight-specific mid-trimester normal median equations for the prenatal serum markers α-fetoprotein (AFP), free β subunit human chorionic gonadotropin (fβHCG), and unconjugated oestriol (uE3) for a Chinese population; to compare and replace the median equations built in LifeCycle software; to evaluate the effect of equations used for gestation correction on estimating risk in Down's syndrome, Edward's syndrome, and neural tube defect (NTD).A total of 353,065 cases of prenatal screening data of pregnant women were screened by 13 prenatal screening institutions in China.
The diagnosis of fetal triploidy should be considered when there is a very high maternal serum alpha-fetoprotein and no ultrasound evidence of open neural tube defect, ventral wall defect, or any other explanation.
Routine maternal serum alpha-fetoprotein screening for neural tube defects, and now also for aneuploidy, is a classic example in which there has been a schism between the clinical expertise to manage such a program within a tertiary level reproductive genetics center and the ability to reach patients in regions that are not routinely accessible to the tertiary center.
In an attempt to identify biochemical components of the genetic predisposition to neural tube defects (NTDs), levels of folate, cobalamin, apo-transcobalamins I and II and alpha-fetoprotein were studied in midtrimester amniotic fluid from 24 pregnant women who had previously had a child with NTD.
We detected neural tube defects (0.2%) as expected but were surprised by the efficacy with which low serum alpha-fetoprotein values identified aneuploid fetuses.
The risk of an open neural tube defect or other serious fetal abnormality was 60% when alpha-fetoprotein levels measured greater than or equal to +3 and 86% for levels greater than or equal to +5 SD.
The increased frequency of hydrocephalus among sibs of probands with a NTD and vice versa suggests that, following the birth of a child with either malformations, subsequent pregnancies should be monitored at mid-gestation by amniotic fluid AFP and serial ultrasound examination.
Neural tube defects are associated with an increase of AFP in amniotic fluid, but, as in normal pregnancies, the values decrease with increasing gestational age.
A severe neural tube defect diagnosed in a 191/2-week-old "at risk" fetus on the evidence of a markedly elevated alpha-fetoprotein level in the amniotic fluid, turned out to be an occipital myelocoele.