Map the window, keep the uncertainty visible.

Naegele’s rule: 280 days from the first day of your last period, which assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter, the due date shifts by the same number of days, and this hub applies that adjustment automatically.

It is the six days ending on ovulation day: the five days before, because sperm survive up to five days in fertile mucus, plus ovulation itself and the day after, because the egg stays viable about 24 hours. The two highest-probability days are the day before ovulation and ovulation day.

Track at least six cycles, then use the calendar rule: the first fertile day is your shortest cycle minus 18, and the last is your longest cycle minus 11. If that produces a window wider than about 12 days, the calendar is not telling you much — ovulation predictor kits or basal body temperature will work far better.

Gestational age is counted from the first day of your last period, not from conception. That is why you are already considered two weeks pregnant on the day you conceive. Enter your date and method and the hub gives you weeks and days exactly, plus the trimester.

For a day-5 blastocyst, the transfer date plus 261 days; for a day-3 embryo, the transfer date plus 263 days. Fresh and frozen use the same offsets. IVF dating is the most accurate available, because the fertilisation date is known exactly, so it should not be re-dated by a later scan.

ACOG Committee Opinion 700 puts a first-trimester ultrasound first, then a known conception or IVF date, then the last menstrual period. If a first-trimester scan differs from LMP dating by more than 5 to 7 days, the scan date is used.

Very, but only in a narrow window. Robinson & Fleming dating from CRL is accurate to about ±5 days between roughly 7 and 14 weeks, when the CRL runs about 10 to 84 mm. After 14 weeks, growth variation makes CRL unreliable and biometry takes over — and the due date is normally not changed again.

The IOM/NASEM 2009 ranges for a singleton, by pre-pregnancy BMI: 28 to 40 lb if underweight, 25 to 35 lb at normal weight, 15 to 25 lb if overweight, and 11 to 20 lb with obesity. Most of it comes in the second and third trimesters — the whole first trimester accounts for only about 1 to 4.5 lb.

It compares the estimated weight against the Hadlock in-utero growth curve for that gestational age. Below the 10th percentile is flagged as small for gestational age and above the 90th as large. Estimated fetal weight carries about 10 to 15% error even in expert hands, so trend across scans matters far more than one number.

Subtract the number of weeks the baby was born early from their chronological age. A baby born at 32 weeks is 8 weeks early, so at 6 months old their corrected age is 4 months — and that is the age their milestones should be judged against, usually until about age 2.

It does, though far less sharply than maternal age. Time to conception lengthens from around 40 to 45, and large cohort studies link advanced paternal age to modestly higher rates of miscarriage and certain neurodevelopmental conditions. The absolute risks stay small; it is a factor to discuss with a specialist, not a deadline.

No. Calendar-based methods have a typical-use failure rate in the double digits, and pregnancy is possible on days the calendar calls infertile — especially if your cycles vary. Use a method designed for contraception and talk to a clinician about which one fits.