Length of pregnancy by week

This graph groups the births by weeks. For instance, "week 40" means days 280-286.

Summary

Excluding inductions, here are the percentages for each week:

• Percentage of babies born at 35 weeks: 1.4%
• Percentage of babies born at 36 weeks: 2.7%
• Percentage of babies born at 37 weeks: 6.4%
• Percentage of babies born at 38 weeks: 13.7%
• Percentage of babies born at 39 weeks: 25.3%
• Percentage of babies born at 40 weeks: 31.8%
• Percentage of babies born at 41 weeks: 16.5%
• Percentage of babies born at 42 weeks: 2%
• Percentage of babies born at 43 weeks: 0.1%

These percentages are based on the 11984 babies born spontaneously, excluding the 3778 babies who were induced. As with the graph, "at 40 weeks" means babies born on 40 weeks, 0 days through 40 weeks, 6 days.

Data Table

Total births: 15762

Week	All births	% of total	Running total %	Spontaneous	% of total	Running total %
35	217	1.4	1.4	169	1.1	1.1
36	417	2.6	4	325	2.1	3.2
37	992	6.3	10.3	770	4.9	8.1
38	2066	13.1	23.4	1644	10.4	18.5
39	3836	24.3	47.7	3037	19.3	37.8
40	4700	29.8	77.5	3808	24.2	62
41	2998	19	96.5	1977	12.5	74.5
42	515	3.3	99.8	241	1.5	76
43	21	0.1	99.9	13	0.1	76.1

The "running total %" basically tells you how many babies have been born by the end of the week. For example, 37.8% of women went into labor spontaneously before they hit week 40.