Accurate conception dating

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 [28].

The American College of Obstetricians and Gynecologists.

Berghella V, et al., Does transvaginal sonographic measurement of cervical length before 14 weeks predict preterm delivery in high-risk pregnancies?

303, February 2014 Society of Obstetricians and Gynaecologists of Canada.

Multifetal gestations: twin, triplet, and higher-order multifetal pregnancies.

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.

Time of implantation of the conceptus and loss of pregnancy.

Daily immunoactive and bioactive human chorionic gonadotropin profiles in periimplantation urine samples.

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.

American College of Obstetricians and Gynecologists.

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