How to Calculate Your Pregnancy

For some women, pregnancy may come as a surprise and for others, something they’ve been hoping for. Either way, once you’ve confirmed your pregnancy, it’s important to be able to know your estimated due date. Knowing when you’re due will allow you to prepare for the baby’s birth and pace yourself accordingly.

There are two ways for you to calculate your due date: You can either base it on the date of conception (if you can recall the specific date) or on the date of the first day of your last menstruation cycle. While these can be fairly accurate when calculating when you’re going to give birth, keep in mind that only 20% of women actually give birth on their estimated due date. In reality 80% of babies are born within ten days of their due date, hence, physicians usually use the estimated due date as the prescribed time when the expectant mother is to enter into confinement in preparation for childbirth.

Calculation Option 1: Last Menstrual Period

Keeping note of your menstrual cycles is especially useful for women who want to get pregnant, as you will be more aware when your ovulation period, also known as the period when you are most fertile.

The average length of time for pregnancy is 40 weeks or 280 days. Starting from the first day of the last normal menstruation cycle you had, count onwards until the 40th week. Add in the one week for your menstruation period to end.

For example, your last menstruation started on January 1st. your estimated due date would be October 8 of the same year, following 280 days. How? You add seven days to the first date (January 1) and you’ll end up with January 8, in consideration of your menstrual cycle. A normal pregnancy will entail a gestation period of nine months, so add nine months to your January 8 and you end up with October 8 as your estimated due date.

Calculation Option 2: Date of Conception

Usually women do not know the exact date of conception, but if you are lucky enough to know, you may end up with a more accurate due date.

Women typically have a 266-day gestation period, which translates into 38 weeks. Check your calendar and count off from the first week onwards. So if your date of conception was on the first of January 2009, your estimated due date would be on September 24, 2009.

Premature and Post term Births

Premature births refer to deliveries that happen too early, usually under the normal gestation period. There is no specific reason on what causes a premature delivery, but they are often associated with:

Multiple pregnancies, or bearing twins, triplets or more
Tobacco use
An abnormally-shaped uterus, which may cause difficulty in childbirth
Placental abruption, the placenta being the fetus’ way of obtaining nutrients from its mother
Severe infections or high fever in the mother
Untreated disease of the thyroid gland in the mother
High blood pressure in the mother
Diabetes in the mother
Kidney disease in the mother

The cause of post term pregnancy, or indeed the factors that influence a late childbirth, is largely unknown. Most cases of post term pregnancy are inaccurate due dates, probably stemming from mothers not being able to state when their last menstruation started or their conception date correctly.

While post term pregnancy poses no risk to the mother, the fetus is in danger of losing nutrients and oxygen as the placenta weakens its ability to transmit these successfully to the fetus. There is also a chance that the babies may inhale their own fecal matter mixed in the amniotic tissue which may result in severe pneumonia. Post term babies will not have the typical appearance of a newborn, as they are likely to have cracked skin, long nails, long hair and even fat tissue under the skin.

Knowing your due date will help you monitor your baby’s development more accurately and tend to its needs accordingly. The sooner you know your estimated due date, the better.