Twin Pregnancy Calculator — Week 39: Di/Di, Mo/Di & Mo/Mo
You are 39 weeks pregnant with twins. Twin gestation deviates meaningfully from singleton pregnancy from week 39 onwards — chorionicity, growth discordance and delivery timing all change. Here is the exact week-39 twin picture.
Twin Pregnancy Calculator
Enter the first day of your last menstrual period (LMP). EDD = LMP + 280 days.
Baby at week 39
Per twin, week 39 development: Full term. All organs ready for outside life. Placenta continues supplying oxygen and antibodies.
Mother's body — what changes
Twin pregnancy at week 39 differs — expect: Nesting instinct peaks. Contractions become regular. Watch for water breaking.
Nutrition & supplements
Add ~450 kcal/day. Increase iron and DHA — brain growth peaks now. Split meals into 5–6 small portions to control heartburn and stable glucose. For twin gestation add an extra 300 kcal on top (total ~600 second trimester, ~750 third), 50% more iron, and split hydration to 3–3.5 L/day.
Safe exercise
Reduce intensity but keep moving. Pelvic floor + squats prepare for labour. Avoid contact sports, ski, horse-riding and hot yoga. For twins reduce intensity 20% earlier — bed rest is not routinely indicated but modified activity from week 24 is prudent.
Doctor visit checklist — week 39
- ✓Full term — labour may start any day
- ✓Chorionicity confirmed at 10–14 weeks (Di/Di, Mo/Di, or Mo/Mo)
- ✓Growth scans every 4 weeks (Di/Di) or every 2 weeks (Mo/Di, TTTS surveillance)
- ✓Maternal-fetal medicine (MFM) referral by week 20
Warning signs — call your provider immediately
- ⚠Heavy bleeding (soaking a pad in an hour)
- ⚠Severe abdominal pain that does not ease
- ⚠Fever above 38°C / 100.4°F
- ⚠Regular contractions before 37 weeks (preterm labour)
- ⚠Reduced fetal movement — fewer than 10 kicks in 2 hours
- ⚠Sudden swelling of face/hands + severe headache (preeclampsia)
- ⚠Bright red bleeding (placental abruption or previa)
Week 39 — Frequently asked questions
How accurate is the Twin Pregnancy Calculator at week 39?
The calculator uses standard gestational-age arithmetic (LMP + 280 days for standard; egg retrieval + 266 days for IVF day-5). Ultrasound crown-rump length between weeks 8–13 is more accurate (±5 days) than LMP — adjust EDD accordingly if the scan differs by more than 7 days.
What size is my baby at week 39?
Approximately the size of a mini watermelon — length 50.7 cm and weight 3290 g per twin (combined weight roughly 1.8× singleton for well-nourished mothers). These are median values from SMFM, ACOG twin guidelines and NICE multiple pregnancy references.
Which symptoms are normal in week 39?
Nesting instinct peaks. Contractions become regular. Watch for water breaking. Every pregnancy is different — call your provider if anything on the warning-signs list appears.
Should I have an ultrasound at week 39?
Full term — labour may start any day. Routine scan windows are: dating (10–13w), anatomy (18–22w), growth (28–32w).
How much weight should I gain by week 39?
Approximately 13.7 kg cumulative if you started at a normal BMI (IOM guideline). Underweight mothers gain more; overweight mothers less. Twin gestation targets 16–24 kg total (higher than singleton 11–16 kg).
Is my twin pregnancy Di/Di, Mo/Di or Mo/Mo?
Chorionicity is confirmed on the 10–14 week ultrasound by looking at the membrane between twins — 'lambda sign' = Di/Di (safest), 'T sign' = Mo/Di (requires TTTS monitoring every 2 weeks), no membrane = Mo/Mo (highest risk, delivery by 34 weeks).
When are twins usually delivered?
Di/Di twins: 38 weeks. Mo/Di twins: 36–37 weeks. Mo/Mo twins: 32–34 weeks by planned C-section. About 60% of twins deliver preterm (<37 weeks) spontaneously.
Content aligned with SMFM, ACOG twin guidelines and NICE multiple pregnancy. Reviewed by Dr. Maria Rehman, MD (OB/GYN). This page is educational and does not replace personal medical advice — call your obstetrician for any concern.