During a twin birth, a few minutes separate the arrival of the two babies. This short interval is enough to establish a birth order recorded in the civil registry. For parents of twins, the question often arises: who will be considered the elder, and on what criteria does this distinction rest?
What the civil registry considers to designate the elder of the twins
The rule is simple. The first twin born is the elder on the birth certificate. The civil registry officer records each child in the chronological order of their arrival, with the exact hour and minute.
This registration does not take into account the position in the uterus or how the birth took place. Whether the first baby is born vaginally and the second by emergency cesarean, the order remains that of the clock.
You can also read on Un P’tit Air de Famille a comprehensive file detailing the family implications of this order of arrival.
One point deserves to be emphasized: the right of primogeniture no longer exists in French law. The order of birth between twins has no legal consequence on inheritance, donations, or parental authority. The two children are treated as ordinary siblings under the law.
Order of birth and order of conception: two different things
A popular saying claims that the last born would be the first conceived. This idea is based on spatial logic: the baby placed deepest in the uterus would have been conceived first but would come out last.
Why this logic doesn’t hold
For monozygotic twins (from a single fertilized egg that split), the question of “first conceived” makes no sense. The two embryos come from the same cell. There is no conception chronology.
For dizygotic twins (from two separately fertilized eggs), fertilization can occur within a few hours of each other. No medical examination can determine which of the two eggs was fertilized first. The position in the uterus at the time of birth depends on multiple factors: fetal movements, volume of amniotic fluid, shape of the uterus.
Attributing primogeniture to the “first conceived” is therefore a myth, not medicine.
When birth alters the expected order
During pregnancy, the medical team identifies the twins by their position: twin A (the closest to the cervix) and twin B. Twin A usually is born first.
But a complication can disrupt this scenario. If twin A is in a poor position or if an emergency cesarean occurs after the birth of the first baby, the final order no longer matches what the ultrasounds predicted. The order of birth results from the circumstances of the delivery, not from a biological hierarchy.
The medical role of birth order in the delivery room
In obstetric practice, distinguishing between the first and second twin does not serve to establish a family hierarchy. The issue is medical.
- Once the first baby is born, the team performs an ultrasound to check the presentation of the second (head down, breech, or transverse). This assessment determines the course of the delivery.
- The time between the two births is closely monitored. An interval that is too long increases the risk of complications for the second twin, particularly fetal distress related to placental abruption.
- The second baby may require instrumental extraction or a cesarean if their position has changed after the first one is born. Each twin thus receives individualized care.
For the healthcare staff, the order serves to organize the care of the second baby, not to resolve a family question.
Symbolic primogeniture of twins: what families make of it
If the law gives no advantage to the elder of the twins, the psychological dimension remains strong. Many twins assert their birth rank, even when the gap is measured in minutes.
Cognitive psychologist Fabrice Bak, a specialist in twins, observes that twins themselves often tend to respect a form of informal primogeniture. The firstborn identifies with a “big” role, while the second sometimes positions themselves as the younger.
Parents play a role in how this distinction takes shape. Some choose never to mention the order of birth to avoid confining each child to a role. Others naturally refer to it without attaching particular importance.
- Primogeniture among twins has no effect on inheritance rights or any administrative procedures.
- Zygosity (monozygotic or dizygotic) does not change how the civil registry records the order.
- The birth rank among twins is a family marker, not a legal status.
In some cultures, tradition conversely attributes primogeniture to the second born, considered the “older” because placed at the back of the uterus. This belief persists in several regions of the world, including Europe until the Middle Ages, before civil registration settled the matter with strict chronology.
The question of who is the elder among twins ultimately relates more to identity than to law. The civil registry establishes an order in a few minutes, but each family decides the weight they give it in daily life.
