Early ultrasound accuracy dating conception
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 timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective study BMJ 2000; 321: 1259-1262. Effects on the probability of conception, survival of the pregnancy, and sex of the baby.
Timing of sexual intercourse in relation to ovulation.
Risk of late-preterm stillbirth and neonatal morbidity for monochorionic and dichorionic twins.
Twin pregnancy: the role of ultrasound in management.
Ameri-can College of Obstetricians and Gynecologists.
Number 4, May 1999 (replaces educational bulletin Number 147, October 1990).
Number 9, October 1999 (replaces Technical Bulletin Number 188, January 1994). The Society of Obstetricians and Gynaecologists of Canada recommends the earliest ultrasound with a crown rump length equivalent to at least 7 weeks (or 10 mm) should be used to determine the gestational age .