32,290,399 deliveries · 2016–2024 · observed rates, not predictions
1. Term cesarean rate. Singleton, cephalic, 37 to 41 completed weeks. Gives the observed cesarean rate for any combination of parity, previous cesarean, completed week, induction, body mass index, maternal age, race and Hispanic origin, and payment source.
2. All births, 22 weeks and over. Every hospital birth from 22 completed weeks, with gestational week by single week, fetal presentation and plurality as variables in their own right. This is the view that shows what the term calculator cannot: how the cesarean rate moves across gestation, and what happens at the edges of viability.
3. Robson groups. Every delivery, every gestation and presentation, classified into the ten groups. Gives the standard ten-group table for any combination of maternal age, pre-pregnancy body mass index, race and Hispanic origin, and payment source: size of group, cesarean rate in group, and absolute contribution to the stratum rate.
4. Compare states. The same ten groups for any two or three states, side by side, with the difference in the overall rate broken down group by group into how much comes from the group being larger and how much from its cesarean rate being higher. Built from CDC WONDER rather than the microdata, because the public use file carries no geography.
The first three open with every menu on Any and narrow only where you choose.
Every figure is a direct count from the National Vital Statistics System natality files. Nothing is modelled, fitted, smoothed or extrapolated. Choose a combination and the tool sums the matching birth records and divides.
Because the classification is applied to routinely collected data rather than to a research cohort, group sizes should be read before any rate, and differences between strata should be attributed first to data quality, then to epidemiological variables, and only then to clinical practice.
United States 2016–2024 · NVSS natality microdata · observed rates, not predictions
All deliveries, every gestation and presentation, classified into the Robson Ten Group Classification System. 32,290,399 deliveries.
Size of group is deliveries in the group over all deliveries in the stratum. Contribution is cesareans in the group over all deliveries in the stratum; it is the absolute contribution, and the thirteen contributions sum to the stratum cesarean rate. Robson's rule: read the group sizes before any rate.
Groups 2b and 4b are prelabor cesarean by definition, so their rate is 100 per cent. Group 9 rests on a birth-certificate presentation code of Other, which is not restricted to transverse and oblique lie, and should not be read as a clean abnormal-lie group. Unclassified is a data-quality indicator, not a clinical group.
The same table, with the cesarean rate column replaced by the birth-certificate item epidural or spinal anesthesia during labor. Contribution is epidurals in the group over all deliveries in the stratum, so the thirteen contributions sum to the epidural rate of the stratum, exactly as the cesarean contributions sum to its cesarean rate.
Group sizes and rates by single year for the stratum selected above. A single year's fluctuation is not a trend; 2020 and 2021 are pandemic years.
Payment source is shown beside race on every result because the two are deeply confounded in United States birth data, and a race-specific rate read without the payer distribution invites the wrong conclusion.
Singleton, cephalic, 37–41 completed weeks. 26,816,980 deliveries. Cesarean rate for any combination of eight characteristics.
A prelabor cesarean is recorded as a cesarean with no trial of labor attempted, so those women never entered labor. The left figure is the rate among only the women who did labor; it is the number relevant to a woman who is expected to labor. The right figure is the share of the whole cell delivered without labor.
Birth-certificate item epidural or spinal anesthesia during labor. The item is also checked on most prelabor cesareans, where the anesthetic was for the operation rather than for labour, so the middle row is the labour-analgesia rate and the top row is not.
Each table varies one characteristic and holds the rest at whatever the menus say, Any included. The two rows above differ in recorded labor onset only. They are not a treatment comparison: women selected for induction differ from women who labor spontaneously in ways birth certificates do not capture.
Payment source is shown on every result because race and payer are deeply confounded in United States birth data, and a race-specific rate read without the payer distribution beside it invites the wrong conclusion.
Obesity is split into class I, class II and class III rather than pooled above 30, because the cesarean gradient continues to rise across those three classes and a single “30 or more” category conceals it.
Nine single years of a fixed cohort. A single year's fluctuation is not a trend; look for sustained directional change across three years or more, and read 2020 and 2021 as pandemic years rather than ordinary observations.
Every publication, definition and exclusion behind the figures
Robson groups. All hospital deliveries, every gestation and presentation, 32,290,399 pregnancies. The unit is the pregnancy, not the baby: a twin pregnancy is one record, because the Ten Group Classification classifies women, and it is counted as a cesarean if either baby was delivered abdominally. Gestational age is the obstetric estimate (OEGest_Comb, positions 499-500) throughout, and no birthweight floor is applied, so periviable births are not silently removed. Nothing is excluded for a missing characteristic; Unknown is carried as a level in the body mass index, race and payment menus, so selecting Any everywhere reproduces the published all-deliveries table exactly.
Term cesarean rate calculator. Hospital deliveries, singleton, cephalic presentation, 37 to 41 completed weeks by the obstetric estimate (OEGest_Comb, positions 499-500), 26,816,980 deliveries. 3.7 per cent of otherwise eligible deliveries are excluded there because one of the eight characteristics is missing or not stated, most often body mass index.
The unit is the delivery, not the infant. A twin pregnancy is one delivery, not two, because the denominator of the classification is the woman. Counting infants would double group 8 and dilute the size and contribution of every other group. The natality file holds one record per infant and carries no maternal identifier, so one record per delivery is selected as every singleton plus the last infant of each multiple set (SETORDER_R = DPLURAL). The last-born is used rather than the first because a pregnancy counts as a cesarean if either baby was delivered abdominally: once the abdomen is open the remaining fetuses are delivered through it, so the route of the last-born is the route of the set. The per-set-order cesarean rate rises monotonically, as that implies (2024: 73.3 per cent for the first of twins, 75.9 for the second). The consequence is that presentation for a multiple pregnancy describes the last-born, not twin A. About 110 multiple pregnancies a year carry no usable set order and are dropped whole rather than counted twice.
Parity. The live birth order recode runs 1 to 9, where 8 means eight or more previous live births and 9 means not stated. Eight or more is carried in the 4 or more parity level and counts as multiparous. An earlier build of this tool tested only 1 to 7, which left roughly 24,000 grand multiparous women a year outside the classification; they are now in Robson groups 3, 4 and 7, and unclassified has fallen from 0.88 to 0.51 per cent of deliveries.
Presentation in a multiple pregnancy is that of the last-born, not of twin A, because the last-born is the record the pregnancy is taken from. Across 2016–2024 that reads 63.9 per cent cephalic, 32.1 per cent breech and 4.0 per cent other, against 75.0, 23.2 and 1.8 for twin A. The public use file carries no maternal identifier, so twin A's presentation and the set's mode of delivery cannot both be recovered; the mode of delivery was given priority. Robson group 8 is unaffected, since it takes every multiple pregnancy whatever the presentation, and every maternal and pregnancy-level variable is identical across a set.
Epidural or spinal analgesia is the single birth-certificate checkbox Epidural or spinal anesthesia during labor, field LD_ANES of the natality file. It is reported for 77.7 per cent of all deliveries in the window and for 77.2 per cent of the deliveries in which labour occurred. It is a checkbox on a certificate, not an anesthesia record: it carries no timing, no indication, no distinction between epidural, combined spinal-epidural and single-shot spinal, and no information on whether analgesia was requested and declined or requested and unavailable.
Parity is the live birth order recode, so parity 0 is nulliparous. Previous cesarean is the birth-certificate risk-factor item. Induction is the birth-certificate labor-characteristic item. A prelabor cesarean is a cesarean recorded with no trial of labor attempted; because those women never laboured, the term calculator reports the cesarean rate twice, once among all women in the cell and once among only those who laboured.
In strict order: plurality greater than one to group 8, any multiple including quintuplet or higher; singleton with presentation coded Other to group 9; singleton breech to group 6 if nulliparous and group 7 if multiparous; singleton cephalic at 36 weeks or less to group 10; term singleton cephalic with a previous cesarean to group 5; and the remaining term singleton cephalic pregnancies to groups 1, 2a and 2b if nulliparous and to groups 3, 4a and 4b if multiparous, by labor onset. Where induction and no trial of labor were both recorded, which is a logical contradiction, induction takes precedence.
Subgroups follow Robson: 2a and 4a are induced labor, 2b and 4b are prelabor cesarean. The correct denominator for the induction rate in group 2 is groups 1 and 2 combined, and for group 4 it is groups 3 and 4 combined, never the group alone.
Size of group is deliveries in the group over all deliveries in the stratum. Cesarean rate in group is cesarean deliveries in the group over deliveries in the group. Contribution is cesarean deliveries in the group over all deliveries in the stratum; it is the absolute contribution, and the thirteen contributions sum to the stratum cesarean rate.
The second ten-group table repeats the first with the cesarean rate column replaced by the epidural rate. Its contribution column is epidurals in the group over all deliveries in the stratum, so the thirteen contributions sum to the epidural rate of the stratum in the same way.
Group sizes should be read before any rate. No group can be interpreted on its own until the relative sizes of the others in the same stratum have been read. Groups 6 to 10 always carry high cesarean rates and always contribute little, because they are small.
Group 9 is defined by a presentation code of Other, which on the birth certificate is not restricted to transverse and oblique lie. Its cesarean rate falls from 58.1 per cent in 2016 to 46.5 per cent in 2024, which is not a plausible clinical trajectory for a true abnormal-lie group and points to abstraction drift. It should not be read as a clean abnormal-lie group.
Groups 2b and 4b are derived rather than recorded. The prelabor cesarean share in United States data has been questioned in print as implausibly high and possibly a misclassification artifact of deriving labor onset from the trial-of-labor item. Those figures should not be read at face value.
Previous cesarean is a self-reported birth-certificate item and is the sole determinant of group 5. Between 884 and 1,117 records a year are coded nulliparous with a previous cesarean; they are assigned to group 5 on the previous-cesarean criterion.
The anesthesia item is checked on 79.7 per cent of the 7,375,328 prelabor cesareans in these data, although those women did not labour and the certificate item is worded during labor. The item is therefore recording operative neuraxial anesthesia as well as labour analgesia. Any rate that keeps prelabor cesareans in the denominator is a mixture of the two and should not be read as a labour analgesia rate; the tables here report both, and the laboured denominator is the one to use.
Body mass index derives from self-reported pre-pregnancy weight and height and is missing for 1.9 to 2.7 per cent of records depending on the year. The cesarean status of a multiple delivery is taken from the first-born infant, so a combined vaginal-cesarean delivery is counted as vaginal, which understates the group 8 cesarean rate by roughly 1.4 percentage points.
The user guide lists the plurality field as running from 1 to 4, but the file also contains the value 5. Bounding the group 8 rule at 4 silently drops those records; the rule used here has no upper bound.
Resident birth totals and the overall cesarean rate reproduce the published National Center for Health Statistics final figures for every year from 2016 to 2024. Every characteristic reproduces the published national distribution: 39 weeks is the modal term week at 37.2 per cent, induction runs at 32.8 per cent, Medicaid at 41.1 per cent, Hispanic origin at 25.0 per cent. Both views were built by separate extraction passes over the microdata and reproduce each other's group totals exactly.
The epidural counts were added by a fresh pass over all 33,589,282 records. That pass reproduced the deliveries, cesareans and prelabor cesareans of both cubes exactly, cell for cell, across all 122,850 Robson cells and all 432,000 term cells, before the new counters were accepted. Neuraxial use in Robson groups 1 and 2a combined runs from 81.8 per cent in 2016 to 87.4 per cent in 2024, reproducing the published nine-year series for those groups.