Pregnancy Metrics

Pregnancy calculators and fetal growth reference tools for educational use.

Methodology

All date math is implemented as pure functions under src/lib/pregnancy-dates.ts. Inputs are calendar dates only (YYYY-MM-DD). Arithmetic uses UTC date-only conversion so local timezones do not shift results by one day.

Core rules

  • LMP-derived EDD = first day of LMP + 280 days
  • Known conception/ovulation EDD = date + 266 days
  • Estimated conception from EDD = EDD − 266 days
  • IVF day-5 blastocyst transfer EDD = transfer + 261 days
  • IVF day-3 embryo transfer EDD = transfer + 263 days
  • Fertilization/egg-retrieval (conception-equivalent) EDD = date + 266 days

Assumptions

  • LMP methods assume roughly 28-day cycles with ovulation near day 14.
  • Actual conception day usually cannot be determined precisely.
  • ART pregnancies should prefer embryo age and transfer date over LMP.
  • Formal obstetric EDD should integrate early ultrasound and clinical records—not these educational tools alone.

Gestational age and trimesters

Gestational age is shown as complete weeks plus remaining days. Educational trimester ranges used here: first through 13w6d, second through 27w6d, third from 28w0d. Clinics may use slightly different cutoffs.

Sources

Dating conventions are aligned with ACOG pregnancy-dating guidance (Committee Opinion on Methods for Estimating the Due Date) and standard educational ART day-count offsets. This site is not affiliated with ACOG and is not an official ACOG calculator.

Formula version: pregnancy-dates-v1