Although the unborn baby is in the womb for approximately 37 weeks, the average length of pregnancy or gestation is 40 weeks. Because pregnancy is measured from the first day after a woman’s last period and not from the date of conception, which is usually two weeks later. The baby settles in the uterus five to seven days later. Because some women don’t know the date of their last period (or have irregular periods), full term is when the baby is born between 37 and 42 weeks after the estimated due date.
A baby born before week 37 is considered premature. However, a baby who is still not born by week 42 or earlier is considered overdue. An overdue baby will often have labour inducing procedures.
The length of the gestation
Human gestation lasts on average 280 days. This is 40 weeks from the day the woman had her last period. EDC (estimated date of confinement) is the medical term for the due day. Only four percent of women give birth on the EDC. You can find many online pregnancy calculators (see Baby due-date calculator ) that will tell you when your baby is due if you enter the date of your last period.
The easiest way to calculate the due date for your period is to add seven calendar days to the last day of your last period and then add nine months. If your last period began on February 1, add seven days (7 February) and then nine months (9 November), for an 8 November due date.
Determining baby due date
Some women may not know when their period began. The following clues can help you determine the length of your gestation:
- Ultrasound examinations (especially when performed within six to 12 weeks)
- Vaginal and abdominal examinations reveal the size of the uterus
- Time when fetal movements first feel (an approximate guide only).
Pregnancy ultrasound
An ultrasound scan of the pregnancy is non-invasive and uses high frequency sound waves to scan the baby and mother. A pregnancy ultrasound can be performed using the following procedures:
- The woman lies down on a table.
- Apply a small amount of clear, conductive jelly to the abdomen.
- The operator places the transducer, a small handheld instrument, onto the abdomen of the woman.
- The transducer moves across the abdomen. The sound waves bounce off the internal structures of the baby and are then transmitted back to the transducer. The sound waves are then converted into a two-dimensional image on a monitor. The sound waves are transmitted to the mother without her being able to feel or hear them.
- The operator can determine the gestational age of the baby by measuring its body parts (e.g. head circumference, length of long bone)
Diagnostic uses of ultrasound during pregnancy
Pregnancy ultrasounds can be used to diagnose many conditions, including:
- Multiple fetuses
- Baby health problems
- Ectopic pregnancy is when the embryo is found in the fallopian tube and not the uterus.
- Placenta praevia is an abnormality in which the placenta sits over the neck of a woman’s womb (cervix).
- The mother’s reproductive health.
Premature babies
Premature babies born before week 37 are considered to be premature. Prematurity of the baby will determine its chances of survival. The baby’s survival chances will increase if it is closer to term (estimated day of confinement or EDC). After 34 weeks of gestation, almost all babies survive.
Many health issues are common in preterm babies, which can be caused by immature organs. Common problems include respiratory difficulties and increased susceptibility for infection.
There is often no known cause of premature labor. However, there are some risk factors that could increase the likelihood of having a baby.
- Smoking or drinking alcohol during pregnancy
- Pregnancy: Low body weight before pregnancy
- Inadequate weight gain during pregnancy
- No prenatal care
- Stress on the emotional side
- Problems with placentas such as placentapraevia
- There are many diseases, such as diabetes and congestive cardiac failure.
- Syphilis is an infection.
Overdue babies
Five out of 100 babies will be past due, which is more than 42 weeks gestation. Your doctor will monitor your condition closely if you are more than one week late than your due date. These tests include:
- Monitoring the heart rate of the fetus
- A cardiotocograph machine is used
- Ultrasound scans.
After 38 weeks, the placenta begins to lose its integrity. This means that an overdue baby might not receive enough oxygen. A baby that is overdue could become too big for vaginal delivery. In general, an overdue baby is inducted once it has reached two weeks before its due date. There are several methods for induction.
- Vaginal prostaglandin Gel – To help dilate your cervix
- Amniotomy is breaking the water, also known as an artificial rupture or membranes (ARM).
- Oxytocin is a synthetic hormone that’s administered intravenously to stimulate uterine contractions.
Where can I get help?
- Your doctor
- Your obstetrician
- Midwife or childbirth educator
Important things to keep in mind
- The unborn baby stays in the uterus for around 38 weeks. However, the average length of pregnancy or gestation is 40 weeks.
- Pregnancy starts on the first day after the woman’s last period. It does not count as the date of conception, which is usually two weeks later.
- Because some women don’t know the date of their last period, it is possible for them to be unsure. A baby is considered full term when it is born between 37 and 42 weeks after its estimated due date.
