Twin Pregnancy (Multiple Gestation)
Twin gestations are classified based on chorionicity (number of placentas) and amnionicity (number of amniotic sacs), which are the primary determinants of fetal risk.
Classification Types
- Dichorionic-Diamniotic (Di-Di): Two placentas, two sacs (e.g., all dizygotic, some monozygotic). Lowest risk.
- Monochorionic-Diamniotic (Mo-Di): One placenta, two sacs. Higher risk (e.g., TTTS).
- Monochorionic-Monoamniotic (Mo-Mo): One placenta, one sac. Highest risk (e.g., cord entanglement).
Maternal & Fetal Complications
| Complication | Details |
|---|---|
| Maternal | Pre-eclampsia, Gestational Diabetes, PPH (due to uterine overdistension). |
| Twin-Twin Transfusion (TTTS) | Specific to Monochorionic twins, blood flow imbalance leads to donor/recipient discrepancies. |
High-Yield Exam Pearl:
- Chorionicity Determination: Most accurately assessed via ultrasound in the first trimester (e.g., “Lambda” or “Twin Peak” sign indicates Di-Di).
- Delivery Timing: Recommended delivery for uncomplicated Di-Di twins is 37–38 weeks; Mo-Di is typically 36–37 weeks.