Twin Pregnancy Calculator — Week 4: Di/Di, Mo/Di & Mo/Mo
You are 4 weeks pregnant with twins. Twin gestation deviates meaningfully from singleton pregnancy from week 4 onwards — chorionicity, growth discordance and delivery timing all change. Here is the exact week-4 twin picture.
Twin Pregnancy Calculator
Enter the first day of your last menstrual period (LMP). EDD = LMP + 280 days.
How to Use This Calculator
1. Enter the LMP date
Use the labelled fields and units that match your situation.
2. Calculate instantly
The result, visual comparison, and working update as values change.
3. Discuss the estimate with your clinician
Check assumptions, then copy, print, or share the calculation.
Practical Examples & Use Cases
| Starting date | Method | Calculation | Planning use |
|---|---|---|---|
| 1 Jan | LMP | +280 days | Estimated due date |
| Known clinical date | Ultrasound | Clinician dating | Confirm or revise estimate |
Baby at week 4
Per twin, week 4 development: Implantation occurs day 6–10 after fertilisation. The blastocyst splits into embryo + placenta. hCG production begins.
Mother's body — what changes
Twin pregnancy at week 4 differs — expect: Implantation spotting possible (light pink/brown, 1–2 days). Home pregnancy test may turn positive at the end of the week.
Nutrition & supplements
Focus on folic acid 400–600 mcg/day (neural tube), iodine 150 mcg, and small frequent meals to counter nausea. No extra calories yet — normal maintenance intake is adequate. 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
150 minutes/week of moderate activity — brisk walking, stationary cycling, prenatal yoga. Stop any exercise that leaves you unable to hold a conversation. For twins reduce intensity 20% earlier — bed rest is not routinely indicated but modified activity from week 24 is prudent.
Doctor visit checklist — week 4
- ✓Take a home pregnancy test; confirm with beta-hCG blood test
- ✓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
- ⚠Sudden loss of pregnancy symptoms + spotting
- ⚠Severe one-sided pain (ectopic pregnancy signal)
Week 4 — Frequently asked questions
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.
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