Featured Research

from universities, journals, and other organizations

Weight Gain Between First And Second Pregnancies Associated With Increased Odds Of Male Second Child

Date:
September 25, 2007
Source:
Harvard School of Public Health
Summary:
Mothers who experienced an increase in weight from the beginning of the first pregnancy to the beginning of the second pregnancy may be slightly more likely to give birth to a baby boy during their second pregnancy.

A slightly greater number of males than females are born worldwide every year. In recent decades, although there are still more baby boys born than girls, there has been an apparent decline in the ratio of male to female newborns in several industrialized countries, including Canada, Denmark, England, Germany, Japan and the United States.

Related Articles


That has led researchers to ask: Are there any factors that can influence the probability of giving birth to a baby boy or girl?

A new study from the Harvard School of Public Health (HSPH) and Karolinska Institutet in Stockholm, Sweden, found that mothers who experienced an increase in weight from the beginning of the first pregnancy to the beginning of the second pregnancy may be slightly more likely to give birth to a baby boy during their second pregnancy.

"The results are provocative because few biological factors are known in humans to influence the chances of either conceiving or carrying to term a baby boy or girl. Our study suggests that maternal nutritional factors might play a role," said Eduardo Villamor, assistant professor of international nutrition at HSPH and lead author of the study.

Some prior studies had looked at what factors might influence the sex ratio, but evidence of causality has been weak. Parental smoking, for example, has been associated with both lower and higher sex ratios. Maternal nutritional status had been studied, but there was little evidence to support a causal relationship with the sex ratio.

One of the hypotheses that the authors of this study wanted to test was whether the increase in maternal obesity in several industrialized countries could play a role in the declining sex ratio. Their study found the opposite--maternal weight gain seemed to favor the birth of boys.

The study population, drawn from the Swedish Birth Registry, included 220,889 women who had successive pregnancies between 1992 and 2004 (live births and stillbirths were included). The researchers analyzed the change in women's body mass index (BMI) between the first and second pregnancies. (BMI is weight in kilograms divided by the square of height in meters.)

The male to female sex ratio of the second pregnancy increased linearly with the amount of weight change from the first to second pregnancy, from 1.024 in women who lost more than 1 unit BMI to 1.080 in women who gained 3 or more units (a male to female sex ratio of 1.000 would indicate an equal number of boys and girls being born). The trend was independent of obstetric complications, maternal smoking, parental age, length of the interpregnancy interval and the sex or survival status of the first-born child.

The data suggest that interpregnancy weight gain appears related to a slight increase in the probability of giving birth to a baby boy during a second pregnancy. The obesity epidemic does not appear to explain the observed decline in the sex ratio in some industrialized countries, which indicates that there are factors still unknown influencing the probability of giving birth to boys or girls.

The authors are careful to note that women should not gain weight to try to influence the sex of their baby. "Weight gain before pregnancy carries significant risks to the mother and the baby, and should not be practiced to influence the odds of having a boy," said Villamor. "Other factors of which weight gain is only an indicator could be at play here."

Sven Cnattingius, professor of reproductive epidemiology at the Karolinska Institutet in Stockholm, Sweden, was senior author of the study.

The study was supported by grants from the Karolinska Institutet. Villamor is supported in part by the National Institutes of Health and the Department of Nutrition at HSPH.

Reference: "Interpregnancy Weight Gain and the Male-to-Female Sex Ratio of the Second Pregnancy: A Population-Based Cohort Study," Eduardo Villamor, Pδr Sparιn, Sven Cnattingius, Fertility & Sterility, online September 24, 2007.


Story Source:

The above story is based on materials provided by Harvard School of Public Health. Note: Materials may be edited for content and length.


Cite This Page:

Harvard School of Public Health. "Weight Gain Between First And Second Pregnancies Associated With Increased Odds Of Male Second Child." ScienceDaily. ScienceDaily, 25 September 2007. <www.sciencedaily.com/releases/2007/09/070924122801.htm>.
Harvard School of Public Health. (2007, September 25). Weight Gain Between First And Second Pregnancies Associated With Increased Odds Of Male Second Child. ScienceDaily. Retrieved March 31, 2015 from www.sciencedaily.com/releases/2007/09/070924122801.htm
Harvard School of Public Health. "Weight Gain Between First And Second Pregnancies Associated With Increased Odds Of Male Second Child." ScienceDaily. www.sciencedaily.com/releases/2007/09/070924122801.htm (accessed March 31, 2015).

Share This


More From ScienceDaily



More Mind & Brain News

Tuesday, March 31, 2015

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

AAA: Distracted Driving a Serious Teen Problem

AAA: Distracted Driving a Serious Teen Problem

AP (Mar. 25, 2015) — While distracted driving is not a new problem for teens, new research from the AAA Foundation for Traffic Safety says it&apos;s much more serious than previously thought. (March 25) Video provided by AP
Powered by NewsLook.com
Smartphone Use Changing Our Brain and Thumb Interaction, Say Researchers

Smartphone Use Changing Our Brain and Thumb Interaction, Say Researchers

Reuters - Innovations Video Online (Mar. 25, 2015) — European researchers say our smartphone use offers scientists an ideal testing ground for human brain plasticity. Dr Ako Ghosh&apos;s team discovered that the brains and thumbs of smartphone users interact differently from those who use old-fashioned handsets. Jim Drury went to meet him. Video provided by Reuters
Powered by NewsLook.com
Many Don't Know They Have Alzheimer's, But Their Doctors Do

Many Don't Know They Have Alzheimer's, But Their Doctors Do

Newsy (Mar. 24, 2015) — According to a new study by the Alzheimer&apos;s Association, more than half of those who have the degenerative brain disease aren&apos;t told by their doctors. Video provided by Newsy
Powered by NewsLook.com
A Quick 45-Minute Nap Can Improve Your Memory

A Quick 45-Minute Nap Can Improve Your Memory

Newsy (Mar. 23, 2015) — Researchers found those who napped for 45 minutes to an hour before being tested on information recalled it five times better than those who didn&apos;t. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Health & Medicine

Mind & Brain

Living & Well

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins