The Baby’s Fetal Age
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The Baby’s Fetal Age

Getting pregnant and expecting a baby is an exciting time for many women. Due dates can vary because every pregnancy is different. Some babies may arrive early, and others take their time to make their entrance.

Getting pregnant and expecting a baby is an exciting time for many women. And the term “gestation” will be used often. Gestation is the period between the time the baby is conceived and the time it is born. Gestational age is calculated from the first day a woman has her last period. Fetal age is calculated from the conception date. Fetal age is usually 2 weeks less than gestational age and is considered the actual age of the fetus1. Since the date of conception is hard to calculate, gestational age is commonly used and measured in weeks from the day of the last period. Doctors also use ultrasounds to calculate the age of the baby. 

How due dates are calculated

pregnancy due date

The most accurate way to find out your due date is to use an ultrasound. This is done in the first trimester and doctors use specific measurements to determine how far along the pregnancy is2. You can do it yourself by:

  • Marking when your last period started 
  • Add 7 days to that 
  • Count backward for 3 months
  • Add 12 months to the date

You get an approximate date on which you will deliver the baby. This calculation assumes that you have regular periods and most pregnancies last 40 weeks or 280 days. Regardless of how conception happened, the due date is an estimated date. Due dates can vary because every pregnancy is different. Some babies may arrive early, and others take their own time to make their entrance. 

Reasons why calculations are important 

Calculating the gestational period is important because doctors want to monitor the pregnancy. You will have a lot of appointments to keep and lots of measurements will be taken. 

If you have irregular periods, it becomes difficult to figure out the due date with the last period method. In such cases, ultrasounds are used to determine the fetal age. Keep in mind that ultrasounds done in the first trimester are more accurate in determining the age of the fetus and the due date. 

What to expect during your gynecology appointment?

taking fundal measurement

At every appointment, your doctor will take a fundal measurement. The distance from the top of the uterus to the pubic bone indicates how far along the pregnancy is. Again, this measurement varies from one woman to another and if the measurements deviate by 3 or more weeks, the due date is recalculated.

Between the 14th and 22nd week, your doctor will order blood tests to check for AFP levels. Alpha-fetoprotein is produced by the body and this fluctuates quite widely during pregnancy. High AFP levels could indicate problems and another cause for the miscalculation of the due date.

Charting the physical development of the fetus

Your baby will constantly change through a typical pregnancy. Growth is charted in three stages, or trimesters. Every three months, you will get a check-up and your doctor will inform you about the changes, in terms of weeks. Expect to see distinct changes in your body as well as the baby as time passes. Even though the entire pregnancy is a 9-month process, a full-term pregnancy lasts 40 weeks3

In the first trimester, the fertilized egg starts to divide, and the amniotic sac is formed. It cushions the embryo. Facial features begin to develop during weeks 5 to 8. You can see tiny buds which develop into arms and legs. The brain and neural tissue along with the digestive tract also form. The second trimester is a calm period in which the expecting mom does not experience morning sickness anymore. Facial features are more defined during this time. You will be able to hear your baby’s heartbeat between weeks 13-16. Hair, nails, eyelids, and eyebrows begin to develop. You will feel your baby begin to move between weeks 17-20. At the end of the 5th month, your baby will weigh about a pound. During the 7th month, the baby begins to respond to stimuli.

trio sonogram frame

The third trimester is the most important part of the pregnancy. Your baby starts to gain weight and add body fat at this time. During the 8th month, the baby starts to move more, and the internal organs are fully developed. The lungs take some time to become fully active. You will notice that the baby’s reflexes are well-coordinated, and he/she can weigh between 5 to 7 lbs on average. 

During the 9th or 10th month, depending on the length of time, you can expect to go into labor at any time. The baby does not move as much because there is less room to do so. You know you are ready to deliver when the baby’s position changes and the head points toward the pelvis. Every pregnancy is monitored through every stage and checkups are more frequent in the last month.

You can put the ultrasound pictures of your baby in a sonogram frame so you can always look back on this wonderful pregnancy journey!

Pregnancy is an interesting time due to all the changes taking place in the body. Talk openly with your doctor about issues and mention any issues that crop up. Keeping up with appointments is important.





Sara Gale

Meet Our KeaMommy Contributor: Sara Gale

Sara loves traveling and exploring new places with her family. She is mom to 2 lovely children and loves bringing them out on adventures.

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