The numbers that do not exist
Some of the figures you will be quoted have no national source at all. Knowing which ones is a skill.
An honest guide has to include the gaps. Here are four places where a number is confidently quoted and no reliable national figure exists.
Episiotomy. There is no national US episiotomy rate, and none can be built, because episiotomy is not an item on the US birth certificate. A search of the entire 2024 natality user guide, 159 pages including every file layout and every worksheet, returns zero occurrences of the word.
The best available national figure comes from a voluntary hospital survey: 3.4% of vaginal deliveries in 2024, among hospitals that chose to report. The same report gives a cesarean rate for low-risk first births of 25.3%, measured across over 1,700 hospitals, against the national figure of 26.6%. That "over 1,700 hospitals" belongs to the cesarean measure, not to the episiotomy one. The gap between those two cesarean rates tells you something about which hospitals volunteer. The 3.4% should always be described as "among reporting hospitals," never as a national rate.
Blood transfusion at delivery. NCHS publishes no national rate for 2024. The row in the table is blank, and at least two states are flagged because more than a quarter of their births happened in facilities reporting no cases at all. Any national transfusion figure sourced to birth certificates should be treated as unsupported.
Severe pregnancy sickness. The reference review states that nausea and vomiting affects as many as 70% of pregnant women
, and that the severe form has been reported to occur in 0.3-10.8% of pregnant women.
That is a 36-fold spread. It reflects the absence of an agreed definition, not real variation in the disease. Narrowing it to one number would invent a precision nobody has.
What women expected of pregnancy versus what they got. No US population study measuring that gap could be found. The idea this whole section rests on, that women are led to expect an uncomplicated pregnancy and then read a complication as personal failure, is clinically obvious and, as far as can be established, has never been measured.
These may be underreported on the birth certificate compared with results from large multi-center studies and nationally representative survey data. For example, the rate of uterine rupture for women with a previous cesarean who delivered singletons at term (37 or more weeks of completed gestation) was 0.32% in 1999-2002 in a National Institute for Child Health and Development (NICHD) 19-institution cohort study compared with 0.08 percent for comparable birth certificate data in 2014.When the agency that publishes a number warns you about it, that warning travels with the number.
"Where does that number come from? Is it a national count or a survey of hospitals that opted in?"
"If nobody has measured this, I would rather you say so than give me a number."