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Avoid conceiving in May – according to results from this new study


Hoping to get pregnant? Although most couples may not actively consider when to conceive, some couples prefer to plan which month they would like their child to be born in. A new study reveals that the month in which you conceive could make a difference to the rest of your child’s life.

In a report published in the Proceedings of the National Academy of Sciences, authors Janet Currie and Hannes Schwandt claim that the size of your baby depends on the month of conception.

The best and worst months to get pregnant

Babies conceived in May are 10% more likely to be born prematurely. Premature babies are more vulnerable to a host of health problems such as lower birth weight, underdeveloped lungs and an increased likelihood of contracting infections due to underdeveloped immune systems. They are also at risk of developing disabilities that may affect them for the rest of their lives.

On the other hand, babies conceived between June and August are amongst the biggest, weighing 8 to 9 grams heavier. The study found that there is also a strong seasonal pattern in pregnancy weight gain, which means that mothers tend to have higher pregnancy weight gains during the summer months and therefore give birth to heavier infants.


The study looked at 647,050 groups of siblings representing approximately 1.4 million children in the US. Therefore, seasonal considerations have to be acknowledged.

In the US, babies conceived in May are likely to be born in mid-February, which is peak flu season there. The data collected in the study provides strong evidence that seasonal influenza might affect the length of gestation and therefore the birth weight of the baby.

In Singapore, flu season also tends to occur during the monsoon months of December to February. Hence, Singaporean women attempting to conceive between March to May should take this information into consideration.


However, the authors also point out that contracting influenza earlier on in the pregnancy could also have detrimental effects on the development of the fetus, that do not necessarily result in shorter gestations or lower birth weights. Instead, there may be risks of lasting cognitive deficits. Mothers should thus take care not to contract the flu during the entirety of their pregnancy.

The impact of a child’s birth month on their achievements

There are other things to take note of when planning the month you’d like to conceive. Some reports, such as this one from the Institute of Fiscal Studies in the UK, state that a difference of a few months can have an impact on the child’s achievements as a student. Children born at the start of the academic year tend to perform better than those born towards the end of the academic year.

In Singapore, this means that babies born in January will have the advantage, as that’s when the school year begins. At the young ages of around 5 to 6, a few months can make a big difference to the development of a child’s cognitive and motor skills. Hence, children who are older than their peers have an early advantage in both studies and sports.


Getting pregnant can already be a struggle for some women, so a healthy baby conceived at any time of the year is always joyful news. However, for those who have more control in planning their family, this information could come in useful.

Free 45 minute fertility consultation

If you and your partner would like to learn more about conceiving, Be Natural is offering a free 45 minute consultation with Marie Otsuka, our fertility coach. In this session, Marie will seek to understand the couple’s situation, and offer insights she’s gained through her 10 years of experience in working with infertile Singaporeans. Slots are limited and on a first come first serve basis; contact us here to schedule an appointment!

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