Robson Group 4a

Where this figure comes from

Every number on this page is computed from the National Center for Health Statistics natality public use files — the anonymous record of every birth certificate filed in the United States. Nine annual files, 2016 through 2024, read directly from the source. Nothing is modelled, fitted, smoothed or predicted: each number is one count divided by another. A twin pregnancy is counted once.

The Robson groups are defined by what is known before the birth begins, and a woman is never reclassified by how her birth turned out. Read the size of a group before you read its rate: breech, twins and unusual lies all have very high cesarean rates and all are small, so they move the national figure hardly at all.

This is not a prediction about any one woman, and it cannot tell you what causes anything. Two items on the certificate — whether labor was induced, and whether labor was attempted before a cesarean — are tick boxes filled in differently from state to state, so read the split between “before labor” and “after labor began” as a good guide rather than an exact figure.

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The twelve groups

Doctors who study cesareans almost never look at one big national number. They split every birth into ten groups, using facts that are known before labor begins: how many babies you have had before, whether you have had a cesarean before, whether it is one baby or twins, which way the baby is lying, how many weeks pregnant you are, and how labor starts. Two of the groups are split in half again, which makes twelve. Every birth in the country falls into one group and one group only.

The system was designed by Michael Robson and is used by the World Health Organization. It is the standard way of comparing one hospital with another fairly, because it compares like with like.

Pick the group you belong to. If you are not sure, the eight plain questions are an easier road — they work out your group for you.

Age, weight and exact week are not part of the twelve groups — they are added on top, inside the group you chose. Leave any of them on All if you would rather not narrow it down.