How to Calculate Your Due Date
The most common way of estimating your due date is by adding 280 days (40 weeks) to the first day of your last menstrual period. This technique assumes that your menstrual cycle is 28 days. Keep in mind that you count both your menstrual period and ovulation as the first two weeks of your gestation. If you deliver on your due date, your gestation is only 38 weeks, rather than 40.
You can also find out your due date through our Due Date calculator.
When unsure of the last day of your period, or when you may have conceived, your doctor may use a physical examination or an ultrasound to estimate your due date.
Why Is Due Date Based on The First Day of Your Last Period?
Medical practitioners usually assume that development of a pregnancy on this day because it’s hard to know the actual date you conceived. Remember that released sperm can last up to three days and conception can occur during any of these.
Once your due date is estimated your doctor will advise you that your baby will be considered full if you deliver up to two weeks before or after the estimated date of delivery (EDD)
What Is a Full Term Pregnancy?
Medical practitioners define a full-term gestation as a pregnancy that lasts between 39 weeks and 0 days and 40 weeks 6 days. An early term pregnancy occurs when you deliver before this period. On the other hand, a late term gestation occurs when you deliver your baby after the full term period.
Causes of Early and Late Term Pregnancy
The particular cause of early or late birth is unclear. However, there are various associated risk factors.
Causes of an early term may include:
- Having a previous early birth delivery
- A pregnancy with multiples
- Problem in the uterus
- Infections of the amniotic fluid or lower genital tract
Causes of a late term may include:
- If you had a prior late pregnancy
- If your baby is a boy
- If it’s your first pregnancy
- If you had incorrect calculations
- If you are obese
Are There Complications Associated with Early and Late Term Pregnancy?
Risks of an early term may include:
- Having a small baby with a relatively large head
- Having a baby with less rounded features
- Having a baby with respiratory distress
- Having a baby with feeding difficulties
- Having a baby with poor temperature control
Risks of a late term may include:
- Increased chances of contracting infections
- Having blood pressure complications
- Having a large baby who may tear your vagina during delivery
- Increased chances of undergoing a cesarean operation
- Having a low amount of fluid
- Increased chances of using vacuum assistance during labour
#Please note that development differs from one child to another.
#Content intended for educational purposes only, and should not be substituted for medical advice from your doctor.
Last reviewed January 2019