Berghella V, et al., Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies? American College of Obstetricians and Gynecologists. 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. In addition, although a woman is most likely to become pregnant if she has sex on the day of ovulation conception may also occur from live sperm still in her reproductive tract on the day of ovulation if she had sex for up to five days before ovulation [26,27]. 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. 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? Determining the Estimated Due Date The estimated due date (EDD or EDC) is the date that spontaneous onset of labor is expected to occur. Conceptional age, menstrual age, and ultrasound age: a second-trimester comparison of pregnancies of known conception date with pregnancies dated from the last menstrual period.
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.
Recording devices, like video cameras, are not allowed. Don't leave it in sunlight and don't laminate it - it will fade.
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.
Ultrasound uses the size of the fetus to determine the gestational age (the time elapsed since the the first day of the last menstrual period).
The accuracy of the ultrasound estimate of the gestational age varies according to the gestational age. Chorionic gonadotropin secretion by human embryos in vitro.