How accurate are dating scans at 16 weeks
Although some DNA test that analyse X and Y chromosomes claim to determine baby's gender as early as 6 weeks of pregnancy, girl and boy babies look very similar on ultrasound scans until around 14 weeks.
At this point it becomes more distinguishable but it isn’t obvious.
A full term pregnancy is considered to be 39 to 40 6/7 weeks regardless of the number fetuses being carried . Chervenak FA, Skupski DW, Romero R, et al: How accurate is fetal biometry in the assessment of fetal age?
Chorionic gonadotropin secretion by human embryos in vitro.
However, if you’re still unable to find out for certain by the 18 week mark, you should be be able to easily find out the sex if you choose to have another ultrasound later on in the pregnancy.
Determining the Date of Conception Because the human egg is capable of fertilization for only 12 to 24 hours after ovulation the date of ovulation may be taken as being the date of conception.
However, ultrasound determination of the date of ovulation has the same imprecision as does the ultrasound estimate of the gestational age and, therefore, a precise date of conception cannot usually be determined as with in vitro fertilization.
The earlier age at delivery of multiple gestations is a reflection of the increased incidence of preterm labor and obstetric intervention for complications such as preeclampsia, abruptio placentae, fetal growth restriction, and increased risk for stillbirth that occurs as the number of fetuses increases [30-33]. Mongelli M, Wilcox M, Gardosi J.: Estimating the date of confinement: ultrasonographic biometery versus certain menstrual dates.
The tendency for multiple gestations to be delivered earlier than singleton pregnancies should not be interpreted that multiples should be assigned an earlier estimated due date.