Fascinating stuff

We've been following the poll on this blog to see what gender everyone thinks the baby will be, and this prompted me to look up what the actual ratio of boys to girls is in the US. Turns out the average is 1049 boys born for every 1000 girls. I wonder if this is built in to our genes through evolution? Men historically die earlier, and during the period when evolution played the biggest role in human development (e.g. when mortality directly influenced conception the most) I can imagine this would be even more of a factor. Death from hunting accidents, scouting and territorial disagreements would be more likely back then than they would be in modern-day San Francisco for example.

So I found that figure in this 2006 study. There's a bunch of other really interesting info in there too. For example:

• Since 1990, Tuesday has been the day with the most births in the US, outnumbering Sunday by nearly 2 to 1. In 2006, that day switched to Wednesday. Sunday births have the lowest C-section rates.
• Since 1990, the percentage of mothers who gain either too little or too much weight during pregnancy has increased from 24% up to 32%. I find this to be a disturbing trend and am not sure why it is happening.
• 22% of births are as a result of an induction
• Breech rates are double in women aged 40 compared to women aged 20 (8% to 4%)
• Contrary to the data presented in The Business of Being Born, the presence of midwives at vaginal births has steadily increased since 1991 and is now almost double at 11%. This is not attributable to any increase in home birth rates (which have stayed steady at about 0.6% of all births).
• C-section rate nationwide stands at 31%
• Pre-term births have increased more than 36% since the early 1980s (!!!!)
• The use of forceps or vacuum extraction has halved since 1990.

There's a bunch more stuff in there including info on birth weight, apgar scores and congenital defects.