How is the delivery date calculated when a woman conceives? How do doctors and technicians at the scan centre determine the approximate date for the baby’s arrival? Do they calculate based on your last menstrual date or the date you actually conceive? Read on for better clarity and understanding.
The Last Menstrual Period (LMP) date refers to the first day of your last menstrual cycle. For women who have regular periods, it is quite easy to calculate the gestational age of the baby using this date.
For women with irregular menstrual cycles, calculating the gestational age based on LMP can be difficult. This is because one cannot be sure about when the ovulation occurred and when the fertilisation happened. In such cases, the doctor will take an average of the previous menstrual cycles to understand the cycle length and calculate the delivery date accordingly.
Though the doctors will calculate the gestational age based on menstrual cycle history and the scans, the baby can be expected a few days earlier or later than the given EDD.
Conception date refers to the date when the conception (fertilisation) happened.
When a woman’s menstrual cycle is regular, the conception date can be easily calculated. Conception can happen only around the ovulation time. Ovulation mostly occurs around the 14th day of a typical menstrual cycle that is 28 days long. So, the conception date for a 28-day menstrual cycle can be anywhere between the 11th and 21st day from the 1st day of her menstrual period.
When it comes to IVF, the conception date can be calculated based on the date of embryo transfer. The embryo is transferred only after successful fertilisation. If the fertility specialist is transferring a Day 3 embryo, the conception date will be 16 days before the embryo transfer. If they are transferring the embryo on day 5, the conception date will be 18 days before the embryo transfer.
Expected Delivery Date refers to the date the baby is most likely to be born. It is quite common for the baby to arrive a few days before or after this EDD. The EDD is usually 40 weeks from the LMP or 38 weeks from the conception date. This is because conception happens around the 14th day of a menstrual cycle, which is 2 weeks from the first day of a woman’s period.
The gestation period for a human foetus is roughly 40 weeks. A foetus reaches full growth around week 37, after which it is known as a full-term baby. In most cases, the birth can happen between weeks 39 and 41.
During these 40 weeks, the fetus is closely monitored through scans to ensure the growth and development are as per expectations. These expectations are based on the age of the fetus. The LMP or conception date helps determine the age of the fetus. Without these dates, it is difficult to be sure if the baby’s growth is age-appropriate.
40 weeks after the LMP or conception date will be the approximate delivery date for the baby. Without the correct date, it can be difficult to estimate the delivery date for the baby. Knowing the EDD can help rule out false contractions, and also be cautious towards the end of the pregnancy.
Estimating the due date for the baby’s delivery can be challenging in the following cases:
● If the LMP or conception date is not known
● Irregular periods
● If the baby is too large or small for gestational age.
Here is a quick round-up of how to calculate the due date with the dates you have:
● LMP – If you know your LMP, add 40 weeks to the date and that is your EDD.
● Conception Date – If you know your conception date you can add 38 weeks or 266 days to the date to get your EDD.
● Ultrasound – If you are not sure of your LMP or conception date, you can take an ultrasound within the first 14 weeks of pregnancy. The healthcare provider will estimate the age of the fetus based on its size. Calculate week 40 accordingly to know your EDD. (If the report estimates the foetus is 7 weeks old, add 33 weeks for EDD)
The expected delivery date for a woman can be calculated using both the LMP and conception date. While LMP is easier to keep track of, identifying the exact date of conception can be a little challenging. Give your doctor the dates you know, and they will use their calculations to give you an approximate EDD.
● The conception date can be estimated by adding 2 weeks or 14 days to your LMP. The conception date can be anywhere between 11 – 21 days from the first day of your last period.
● If you don’t remember your LMP, you can try tracing it back to the previous cycle by using the length of your cycle. Your doctor can narrow down the date using ultrasounds to check the baby’s growth and development.
● Let your healthcare provider know your LMP and the average length of your menstrual cycle. Once you miss your period, you can take a pregnancy test to confirm the same. Your healthcare provider will roughly add 40 weeks to the LMP and give you an expected delivery date. You can deliver a few days before or even after this date.
● Some factors that influence the pregnancy due date are the last menstrual period date – the first day of the period, the length of your menstrual cycle and ultrasounds. In the case of IVF, the doctor will have a more accurate date based on the embryo transfer.
