Is Having Four Girls in a Row Unusual?
No, having four consecutive female births is not highly unusual—it occurs by chance alone in approximately 1 in 16 families (6.25%), which is common enough that many families will experience this pattern. 1
The Mathematics of Sex Determination
The probability of having four girls in a row is straightforward to calculate:
- Each birth has approximately a 48.6% chance of being female (the complement of the 51.4% male birth rate) 1
- Four consecutive female births = 0.486 × 0.486 × 0.486 × 0.486 = approximately 5.6-6.25% 1
- This means roughly 1 in every 16-18 families with four children will have all girls purely by chance
Evidence Against Biological Predisposition
Large population studies definitively show that sex determination is a random process with no parental predisposition toward producing children of one gender. 1
Key findings from a comprehensive Scottish study of 549,048 births:
- The sex ratio remained constant at 1.06 (51.4% male) across all birth orders 1
- The probability of having a male or female infant was completely unrelated to the genders of preceding siblings (P > 0.20 for second through fifth deliveries) 1
- No variation was found with maternal age, maternal height, paternal social class, year of delivery, or season of birth 1
The Behavioral Explanation
Families with children all of one sex appear more common than expected not because of biology, but because of parental behavior—these families are more likely to continue having children in hopes of having a child of the opposite sex. 2
Norwegian registry data covering over 540,000 women demonstrated:
- Women with two children of the same sex had a 14% higher probability of having more children compared to women with mixed-sex children (RR=1.14) 2
- This pattern persisted for mothers with three children (RR=1.15) 2
- The sex composition of already-born siblings had no influence on the sex of the next child 2
Clinical Context
The baseline sex ratio at birth is approximately 0.515 in favor of males (51.4% male, 48.6% female), and this ratio can be influenced by various stressors, but not by parental characteristics or previous children's sex 3, 1. Environmental pressures such as pandemics, natural disasters, and economic crises may temporarily affect population-level sex ratios through differential fetal survival, but these effects do not create individual family predispositions 3.
Bottom Line
Having four girls in a row is a normal chance occurrence that happens in approximately 6% of four-child families. There is no evidence of biological mechanisms that would make some parents more likely to have children of one particular sex 1. The appearance of more same-sex families simply reflects that these families tend to have more children overall 2.