My friend and colleague Christopher Marcum is expecting his first child (congratulations, Chris!) and “wanted to know what the timing of births looked like throughout the day.” So, he pulled 2012 births data from the Centers for Disease Control and produced an eye-catching series of plots. Each dot represents the total number of births that occurred in 2012 at each minute between 12:00 a.m. and 11:59 p.m. (1,440 total minutes represented). The colors represent different groups; for example, birth number in the parity graph.
Like any good data scientist, Chris then “ran a model that incorporates a host of information ([mother]’s age, due date, baby’s sex, etc) and came up with a prediction that [my child] will be born at minute 791, or roughly 1:11 p.m.”
What do data for North Carolina show? In 2012, there were 121,820 births with information about time of delivery. Because the NC birth data set is much smaller than the full national dataset that Chris used (3.3 million), I limited my analysis to mode of delivery. Two-thirds of North Carolina births (66%) were “spontaneous” delivery, meaning there was no need for forceps, vacuum, or other instruments and 31% were cesarean section. The remaining 3% were births that required forceps or a vacuum or whose method was unknown; I excluded these from my analysis due to the small sample size.
Chris noted that the “cesarean” effect is “drastic,” and it is, indeed. Among all North Carolina births, half occurred by 12:48 p.m. Among only cesarean births, half occurred before mid-day (11:53 a.m.). Spontaneous births occurred a little later: half occurred by 1:19 p.m.
Some cesarean sections are planned—either due to pre-existing conditions that indicate medical necessity or at the request of the mother—and this element of scheduling is evident in the cumulative distribution of births throughout the day. Compared to spontaneous births, there are far fewer cesarean births that occur before 8:00 a.m.
Half of all cesarean births occur in an 8 hour window, between 8:20 a.m. and 4:27 p.m. In contrast, the range for spontaneous births is 2 hours or 25% wider: half of spontaneous births occur between 7:50 a.m. and 6:03 p.m.
Data are the North Carolina Vital Statistics Births 2012 data from the State Center for Health Statistics. The data were retrieved from The Odum Institute’s Dataverse Network at UNC. Birth records without time of birth were excluded from the analysis (n=693). The analysis also excluded individuals whose delivery involved forceps (n=776) or vacuum (n=3,061) or whose delivery method was unknown (n=62) due to small sample size.