sing ultrasound, and through physical examination. Though the actual timing of delivery cannot be known, the three-step process helps you predict the likely date of birth.
1. Physical examination:
You can know your pregnancy week by the size of the uterus. Around 12 weeks, your medical practitioner can feel the uterus (fundus) above the pelvis. After 18 weeks, the distance (in cm) between the fundus and pubic bone will be the same as the number of weeks from the last menstrual period. In about 20 weeks, the fundus is at the umbilicus. This gives a rough idea about the pregnancy week. However, this is not always the right way to predict the gestational age due to factors such as twin pregnancy, obesity, uterine tumors, or the fundus being higher or lower (5).
2. Ultrasound dating:
Ultrasound works even when you are not aware of the LMP or if your periods are irregular. It is based on a series of measurements of the gestational sac and the fetus.
The sonographer measures the baby from head to toe. This gives the crown rump length or CRL. It helps the doctor estimate the pregnancy week based on the growth of your baby (6).
If there is not much difference between ultrasound measurements and LMP, the doctors may use the LMP to establish the due date. For instance, if your first-trimester ultrasound and LMP estimates fall within the same week, LMP is considered final. If there is a difference of one week or more, the ultrasound estimate is considered (4).
Try our pregnancy due date calculator to know your due date. It gives you the estimated conception date and estimated due date along with the weeks of each trimester. It will also show your current pregnancy week, and many more weeks you have to reach a full-term pregnancy.
[ Read: Growth Scan During Pregnancy ]
Pregnancy Due Date Calculator
When Do You Start Counting Pregnancy Weeks?
You can start counting pregnancy weeks as soon as you calculate your due date based on your LMP. You will be counting your 40 weeks from the first day of LMP. As you near the due date, you may have to start counting your pregnancy by days as – 39 weeks one day, 39 weeks two days, and so on (6).
What If Your LMP is Not Known Or Periods Are Irregular?
The due date calculation works ideally if your periods are regular, i.e., follow a 28-day cycle.
If your periods are irregular or you do not remember your last period, you should wait for your first ultrasound pregnancy scan. Also known as dating scan, it will provide the number of weeks remaining for your due date (7).
If the scan does not give the correct results, your doctor may ask you to wait for some more time. Ideally, the dating scan will be done between ten and 13 weeks plus six days (8).
What Are The Three Trimesters In Pregnancy?
The pregnancy period is divided into three, three-month segments, known as trimesters. The division helps understand the changes in the body.
First trimester: It lasts from week one to week 13, when you experience nausea and tiredness.
Second trimester: It lasts from week 14 to week 28. You will feel much better in this period and your pregnancy bump will be seen. Early pregnancy symptoms such as morning sickness, headache, dizziness, fatigue, etc., slowly disappear.
Third trimester: It lasts from week 29 until you birth the baby. You will require extra energy to help your baby grow and beat the tiredness (9).
Does Pregnancy Really Last For Nine Months?
It is based on calculation. 40 weeks adds up to nine calendar months (with 30 or 31 days each) or ten lunar months (with 28 days each) (10).
For instance, if your last period was on January 1, your estimated due date would be October 7 or 8. It equals to nine months and one week (and can be longer if you go beyond the due date).
[ Read: When Is The Best Time To Get Pregnant ]
How Do You Calculate Pregnancy Weeks After IVF (In Vitro Fertilization)?
Calculating weeks of pregnancy and the due date is more precise during an IVF than natural conception. This is because the exact date of embryo transfer or ovulation is known. The insemination or egg retrieval method is s