Calculating a due date
Calculating the Due Date for Your Pregnancy (Know What to Expect).
At some stage during your pregnancy, you’ve probably asked the question “when is my baby due”. If that’s the case, you’re not alone. Knowing in advance when your baby is coming is critical for you and your partner to get your affairs in order before the big day.
So, if you’re looking for a pregnancy calculator, you’ve come to the right place. Below, we’ll outline the timelines you can expect when giving birth to your child and the different methods we use to calculate that final date.
First day of your last period.
The majority of pregnancies last approximately 38 weeks from your conception. Probably the best way to calculate your due date is to count 280 days from the first date of your last menstrual period. An easy way to do this is to take away three months from the first day of your most recent period, and then add another 7 days.
Remember, this is only an estimation. It is not a surefire absolute deadline. Only very a small number of babies are actually born on their estimated due date. In fact, data from 2017 indicated that 8.7% of babies in Australia were born prematurely.
Use your conception date.
If you know the date of your conception, this can help you figure out when your baby is due. In this regard, you can actually use a conception date calculator to work out your pregnancy due date. You will need to add 266 days to your conception date out your due date (once again, this is an estimation and not a ‘cut-off’ date)
Look at your IVF ‘transfer date’.
You can also calculate your due date if you conceived through in-vitro fertilisation (IVF). This involves looking at your ‘transfer date’, meaning the date your embryo was transferred.
Most transfers happen 3-5 days after egg retrieval. If your transfer was a ‘day-three’ transfer, then you would need to add 263 days from the transfer date. You would add only 261 days if you had a ‘day-five transfer’.
I don’t remember my last period – how far along am I?
Maybe you’ve forgotten when you last had your menstrual period (and perhaps when you conceived). If that’s the case, no need to worry. You can look to other factors and clues to assess your pregnancy due date in these circumstances
For example, you can:
Get an early ultrasound.
Whether you will receive an early ultrasound ultimately will depend on the medical professional you see. Some perform them as a matter of routine. But others will only perform them if you’re experiencing irregular periods, you’re over the age of 35, your due date cannot be estimated because of your physical examination or if you’ve suffered miscarriages in the past.
Look at when you first heard your baby’s heartbeat.
This can give you some indicator that your baby is due. Generally, you’ll hear this after 9-10 weeks of becoming pregnant.
Look at your uterus size.
This can also be a factor in assessing your estimated due date.
The best estimated due date calculator is your obstetrician!
If you’re looking for assistance in navigating your pregnancy and need advice as to how to prepare for your due date, ask a professional obstetrician to get all your answers.
Dr Caroline Hoggenmueller is an experienced obstetrician in Melbourne who can advise on all aspects of your pregnancy from general obstetric care to fibroid removal. She’s delivered over 2,000 babies and counting, while well-versed on estimating the due date of your pregnancy.
Book your appointment with Dr Caroline in her Heidelberg and Bundoora rooms and get an appointment this week. She offers 24/7 one-stop pregnancy care, allowing you to avoid months of waiting lists for the advice you need immediately.