Risk of Twin Pregnancy with Family History
The risk of having twins when you are a dizygotic (fraternal) twin yourself is moderately increased at approximately 1.3 times the baseline risk, while being a monozygotic (identical) twin increases your risk of having monozygotic twins by approximately 1.5 times. 1
Understanding the Genetic Influence
The inheritance pattern of twinning depends critically on which type of twin runs in the family:
Maternal Dizygotic Twin History
- Women who are themselves dizygotic twins have a 30% increased risk of having twins (relative risk 1.30,95% CI 1.14-1.49) 1
- This increased risk appears to be entirely due to dizygotic (fraternal) twinning, not monozygotic twinning 1
- The mechanism involves inherited tendency for hyperovulation (releasing multiple eggs)
Maternal Monozygotic Twin History
- Women who are monozygotic twins have a 47% increased risk of having same-sex twins (relative risk 1.47,95% CI 1.10-1.97) 1
- This manifests as an excess of monozygotic twin births (39 pairs observed versus 18 expected) 1
- This finding suggests genetic components influence both dizygotic AND monozygotic twinning independently 1
Important Caveats
Paternal Family History
- Paternal twin history does NOT increase the risk of twins in the pregnancy, as men do not ovulate
- Only maternal genetics influence the likelihood of hyperovulation leading to dizygotic twins
Baseline Twin Rates
- The natural incidence of twin pregnancies follows Hellin's law: approximately 1 in 89 pregnancies 2
- Twin pregnancy rates have been rising substantially due to assisted reproductive technologies 3
- Dizygotic twins comprise approximately two-thirds of all twin pregnancies 3
Other Risk Factors Beyond Family History
Additional factors that increase twin pregnancy risk include 2:
- Advanced maternal age
- Higher parity (number of previous pregnancies)
- Use of ovulation-stimulating medications (clomiphene, gonadotropins)
- Recent discontinuation of oral contraceptives
- Race (higher rates in certain populations)
Clinical Implications
If you have a family history of twins, early ultrasound confirmation is essential 2:
- Twin gestation sacs can be visualized by 6 weeks gestation
- Two embryos with fetal heart rates visible by 7-8 weeks
- Early diagnosis allows for appropriate risk stratification and monitoring 3
Twin pregnancies carry significantly higher risks including 3:
- 5-fold increase in fetal death
- 7-fold increase in neonatal death (primarily from prematurity)
- Increased maternal complications including preeclampsia, hemorrhage, and cesarean delivery 4