How due date is calculated
The most common method is Naegele's rule: due date = first day of last menstrual period (LMP) + 280 days. This assumes a standard 28-day cycle with ovulation on day 14. For longer or shorter cycles, the calculator adjusts by the difference.
From conception date, the math is simpler: due date = conception + 266 days (since conception happens about 14 days after the start of the LMP).
Early ultrasound dating (6–10 weeks) is more reliable than calculations from LMP, especially for irregular cycles. If your obstetrician revises your due date based on ultrasound, use that date going forward.
Antenatal care in Pakistan
Most Pakistani obstetricians follow a schedule similar to international guidelines: monthly antenatal visits to 28 weeks, fortnightly to 36 weeks, then weekly. Key milestones include the dating scan (6–10 weeks), NT scan (11–14 weeks), anomaly scan (18–22 weeks), and growth assessments in the third trimester.
Important supplements during pregnancy include folic acid 400–800 mcg daily (from preconception through week 12), and iron + calcium from the second trimester onwards. Vitamin D deficiency is widespread in Pakistan — most obstetricians recommend supplementation throughout pregnancy.
FAQ
How is the due date calculated?
The estimated due date (EDD) is calculated using Naegele's rule: LMP + 280 days (for a standard 28-day cycle). Adjustments are made for shorter or longer cycles. From the conception date, EDD = conception + 266 days. Early ultrasound dating is more accurate, especially for irregular cycles or PCOS.
How accurate is the due date?
Only about 5% of babies are born on the exact EDD. Most babies arrive within 2 weeks before or after. The EDD is a guide for monitoring pregnancy progress, planning antenatal visits, and timing scans — not a fixed delivery date.
What if my cycle isn't 28 days?
The calculator allows you to set your cycle length. If your cycle is 32 days, ovulation typically happens around day 18 (not day 14), so the EDD is adjusted 4 days later. For very irregular cycles or PCOS, an early dating ultrasound (6–10 weeks) is more reliable than menstrual dates.
How are trimesters defined?
First trimester: weeks 1–13. Second trimester: weeks 14–27. Third trimester: weeks 28–40. Each trimester has different antenatal priorities — the first focuses on confirming viability and screening; the second on the anomaly scan and routine checks; the third on monitoring growth, position, and readiness for delivery.
When should I have my first antenatal visit?
In Pakistan, the first antenatal visit is usually recommended as soon as you confirm pregnancy (positive test), ideally before 12 weeks. Early visits include confirming the pregnancy, dating ultrasound, baseline blood tests (Hb, blood group, hepatitis, HIV, rubella, sugar), folic acid supplementation, and screening for risks.
What antenatal visits should I expect?
A typical Pakistani antenatal schedule is: monthly visits up to 28 weeks, fortnightly from 28 to 36 weeks, then weekly. Key scans: dating scan (6–10 weeks), nuchal translucency / NT scan (11–14 weeks), anomaly scan (18–22 weeks), and growth scans in the third trimester as needed.