How To Calculate Pregnancy Weeks After IVF

How To Calculate Pregnancy Weeks After IVF
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Many women will want to know their due dates as they will want to prepare themselves mentally and physically for childbirth. Unlike a natural pregnancy, where you won’t know the exact date of fertilization, you will know the exact date of fertilization and implantation in IVF.

This can help doctors calculate the exact date for childbirth. In this article, let’s look into due date calculation in IVF and the formulae you can use to calculate the day of childbirth. how to calculate pregnancy weeks after ivf

Due date calculation for IVF pregnancies

When it comes to knowing your pregnancy due date, IVF is the only case where you and your doctors can be sure about the day of childbirth.

In a natural pregnancy, you won’t know the exact day your egg is fertilized and will only realize that you are pregnant after some days or a month. You will only have an approximate date of fertilization, so your doctor can only give you an approximate date for childbirth.

For IVF, however, your IVF doctors know exactly when the egg was fertilized and transferred into the uterus. This makes it easier for them to calculate the due date accurately.

Here are the formulae you can use to calculate the due date of your IVF pregnancies. The dates are the same for both IVF and ICSI.

Type of transfer Type of IVF Formulae
Fresh embryo transfer
IVF with own eggs, IVF with donor eggs, IVF with donor embryo
Egg retrieval date + 266 days
Frozen embryo transfer (FET)
3-day transfer (cleavage), 5-day transfer (blastocyst).
Transfer date + 266 days − 5 days Or Transfer date + 261 days

Note: In frozen embryo transfer, if the transfer takes more than 5 days after fertilization, subtract that many days from 266 to get your due date.

For example, if the embryo was transferred on the 7th day, subtract 7 from 266 to get your due date.

Transfer date + 266 days − 7 days OR
Transfer date + 259 days

How accurate are IVF due dates?

Whether you got pregnant through IVF or natural intercourse, the due dates may vary from the calculated date. Though most of the time, the due date calculated for IVF is right, they may differ and go up or down depending on the mother and baby’s condition.

How to Count Pregnancy Weeks

Pregnancy weeks are typically counted from the first day of the last menstrual period (LMP). This means the gestational age includes the two weeks before conception actually occurs. The total duration of a pregnancy is considered to be about 40 weeks or 280 days from the LMP. Healthcare providers use this method because it’s often difficult to determine the exact date of conception. Ultrasounds can also be used to estimate the gestational age of the fetus, especially if the LMP is not known or irregular cycles are present.

How do you calculate your due date if you get pregnant without IVF?

Your last menstrual period (LMP), the date of conception, if you know it, or the date of your first ultrasound scan, if you have an early one, can all be used to determine your due date if you become pregnant naturally.

Factors affecting the due date

As we saw above, IVF pregnancy due dates are not always accurate. It has been estimated that only about 5% of mothers deliver their babies on the exact date as the due date. Various factors can affect a woman’s due date. Below are some of them.

  • The mother’s health condition
  • The baby’s speed of growth
  • Age of the embryo (for frozen embryo transfer)
  • Type of pregnancy (single baby, twins, triplets, etc.)


Whether you had an IVF or natural pregnancy, due dates may differ from those given by your doctor. There is no way to ensure a due date, not even with IVF or ultrasound scans.

Due date calculations are just a way to give you a window of time when labor is most likely to start. With this calculation, you can learn and prepare yourself for childbirth.


In a natural pregnancy, you don’t know the exact date and time of conception. This allows you only to guess the approximate date of delivery.

On the other hand, with IVF pregnancy, doctors know the exact date and time of fertilization. This allows them to calculate the accurate date for delivery.

On average, only around 5% of babies are born on the exact date as the due date. Other babies vary by one or two days.

Yes, you can select the baby’s sex in IVF. Actually, IVF is the only way you can choose whether you want a male or female baby. Though most parents don’t ask for this, some parents might wish to have a male or female baby.

Pregnancy symptoms start about 1–2 weeks after embryo implantation. However, you should know that not all women experience pregnancy symptoms after 2 weeks of implantation.

So, you don’t need to worry too much if you don’t experience any symptoms. Visit your fertility doctor and take a blood test or ultrasound to confirm pregnancy.

Picture of Dr. Rukkayal Fathima
Dr. Rukkayal Fathima

Dr Rukkayal Fathima, India's Leading Gynaecologist and the best fertility doctor in Chennai. She has 11+ years of experience and treated 1000+ patients. She finished her M. S., Obstetrics and Gynaecology from the Institute of Obstetrics & Gynaecology (Madras Medical College), Chennai. She is a visiting consultant at St. Isabelle Hospital, Motherhood Hospital, Rainbow Hospital & Mehta Hospital. Dr Rukkayal Fathima specialises in Obstetrics care, Early Pregnancy Scan, IVF, ICSI, TESA/Micro TESE, Menopause advice, Gynaecological surgeries and endoscopy. She is a Co-Founder of Hive Fertility, the Best Fertility Center in Chennai.

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