Updated: 2019, Jul 6

The Beginner’s Guide to Pregnancy Calculator

The Beginner’s Guide to Pregnancy Calculator

Pregnancy‘- a word we are most familiar with when a woman carries a little angel inside her! It’s alternately called gestation or gravidity. A woman is pregnant when she shelters an offspring & let him/her grow inside her slowly & gradually. During the pregnancy period an embryo or fetus develops inside the uterus of the mother.

Symptoms found in a Pregnant Woman

Generally, the length of pregnancy is 37- 42 weeks depending on the nature of menstruation cycle. The average length of pregnancy is estimated as 40 weeks. A baby born prior to 37 weeks is considered premature. On the other hand, a baby which still hasn’t born by 42nd week is called overdue. Both the cases are unexpected & a healthy delivery occurs within 40 weeks. The pregnancy period consists of three trimesters.

  • 1st Trimester: 0-13 weeks. It includes conception.
  • 2nd Trimester: 14-26 weeks. The fertilized egg travel down the fallopian tube & attaches to uterus.
  • 3rd Trimester: 27-40 weeks. It lasts till the birth of the baby.

Pregnancy is tested by detecting the presence of HCG (Human Chorionic Gonadotropin) in women’s blood or urine. GCG (Glucagon Gene) is a hormone which is present in a woman as soon as she’s pregnant. The first home test kit for HCG test was invented by Margaret Cranein 1968 in New York. It contained a vial of purified water, an angled mirror, a test tube. Doctors calculate the early pregnancy of a woman by blood or urine test, where he mainly tests to check if the existence of HCG is found & its amount.

Ancient Pregnancy Calculating Methods

Pregnancy Calculating Methods

Prior to the invention of modern techniques, pregnancy tests was being tested in different ways. Some historical methods are given below. Have a look, they are interesting!

A) The Wheat & Barley Test:
This is one of the earliest home pregnancy testing methods which came from Egypt. The woman had to urinate on wheat or barley seeds over the course of several days. If wheat sprouted, it was a female & if barley sprouted, it was a male child! But if sprouting didn’t occur, she wasn’t pregnant.

B) The Onion Test:
If a woman who is suspected to be pregnant inserts an onion or strong-smelling vegetable inside her vagina overnight & if her breath smells like that onion the next morning, she wasn’t pregnant. If she was, her womb would’ve been closed. So, no smell could be found!

C) The Latch Test:
If a woman is pregnant, she is said to urinate in a basin & then a latch is put in the basin with the urine for three or four hours. After that, the urine is thrown away & the latch is removed. If the impression of the latch is visible on the basin, the woman is pregnant!

Pregnancy Calculator

When a woman gets pregnant, she needs to have clear idea about the month & date of her delivery to give her baby a secure start to its new life! Ovulation calculator, due date calculator, pregnancy conception calculator & weight gain calculator are all pregnancy calculators. The pregnancy calculator determines the pregnancy schedule based on the due date. It’s important to keep track the development of pregnancy. To know the due date we will use a due date calculator.

Ovulation Calculator

Ovulation is a part of female menstruation cycle where an ovum/female gamete is released or discharged by matured ovarian follicle. When the brain release luteinizing hormone (lh) or follicle stimulating hormone (fsh), discharge occurs. But if the female gamete is fertilized by the male gamete, menstruation stops & it’s the time when pregnancy starts. Generally it takes 6-12 days after the egg being fertilized. The ovulation date is 14 days before the first day of your next period. The calculation of this date is necessary because it determines the corresponding due date which is a must need to know the projected date of delivery of the baby.

Procedure of Due Date Calculation

Due Date Calculation

The father of the 40 weeks ‘due-date was a German physician named Franz Karl Naegele (1778-1851). According to him:

-In case of regular menstruation, the task is easy. Average human-pregnancy lasts about 280 days from the first day of the last period. So, you can easily circle out the date if you know that. There is an alternate way. In that case, you have to add 7 to the first day of the last period & then count 3 months back. So, if the date is 5th June, 2000; the due date will be 12th March, 2001. Happy counting!

-& in case of irregular menstruation, a regular pregnancy calculator may not show reliable result. In this case, take the first date of the last period & add 37 weeks to that. The doctor can suggest for the Ultrasound effect. It will determine the diameter of the head of the baby as well as the abdominal circumference. Thus, it will calculate the gestational age. Using ultrasound is the best & most perfect procedure of calculating the expected date of delivery in between the weeks of 8-18.

Gestation Age by Ultrasound/Ultrasonography

Ultrasounds are called diagnostic solography or ultrasonography which is used to see inside the body of the pregnant woman to see the position of the baby as well as its size & condition. It’s by far the most perfect method of assessing gestation age.Ultrasound was first used in clinical purpose in 1956 in Glasgow. Ian Donald (1910-1987), a Scottish physicist, first encouraged the use of ultrasound in pregnancy calculation.

In the first trimester, the body of the fetus don’t get any visible structure to distinguish its different parts. By using ultrasound, we can get the diameter of the sac. A common method to determine MSD i.e. mean sac diameter is by calculating the mean of three sac diameters. Then gestation age (GA) determined by consulting a table. An alternate but simple method is to add 30 to the sac size in mm to find the gestation age in days. By the time the embryo is visible, sac diameter will not be a valid option for determining the gestation age anymore.

GA in the first trimester is normally measured from the fetal crown rump length shortly CRL. This is the longest length of the fetus without limbs & yolk sac. The following formula relates GA (in weeks) with CRL (mm).

GA = –0.0007 (CRL) 2 + 0.1584 (CRL) + 5.2876

In the second trimester, the best parameters are biparietal diameter (BPD) & head circumference (HC) which are related to the GA. Determination of GA (in days) is related to BPD (mm) is done by the formula:

GA = 39.1 + 2.1 (BPD)

Lastly, in the third trimester, fatal biometry subjects to greater individual size variations than in the 2nd one. But its accuracy for GA assignment is reduced gradually. The estimates may have ‘confidence interval’ of more or less than 3 weeks.

Delivery Date by Combination

Delivery Date By Combination

it’s a common practice to combine last menstrual period with ultrasonographic date which is called 10day rule. It’s very easy to understand.

In the 10day rule both of the dates are in agreement of 10 day. If it’s within ten days then the last menstrual period is accepted. But if it exceeds 10 days, ultrasonographic dates are used. This is a common practice in US & Australia.

Pregnancy Conception Calculation

Conception is a term used when a male gamete unites with the female gamete for the purpose of fertilization. Conception occurs in the ampulla of the uterine tube. During intercourse, the mucus is wet & the sperm makes its way in the fallopian tubes where it fertilizes the emerging egg. It takes the sperms about 40 minutes to reach the tubes. In general, sperm can live inside female body for about 3-5 days though their mobility starts to decrease right after 3 days. Conception determines the conception window depending on individual’s cycle. The three-day conception window is best for getting pregnant. On the other hand, a woman can only conceive within the ‘fertile window’ which is 6 days long; 5 days of sperm’s stay inside woman body & the day of ovulation. So, pregnancy conception calculation is of great importance.

You May Also Like: Menstruation and Pregnancy – All Questions Answered

Increased Weight Calculator

When a woman gets pregnant, she’s supposed to gain more weight. The weight gaining calculator assigns the ideal weight during pregnancy depending on height &weight before pregnancy. It’s a prime concern for you to control your diet & keep the weight perfect for a healthy delivery of your baby. Nutritious foods & proper rest are must needs!


so, there is a wide range of pregnancy tests or calculations from which we can get detailed information of the whole pregnancy cycle. Ultra sonogram is a safe & painless procedure to know the condition of the baby inside the womb. The gender of the baby can also be determined through this procedure, generally after 7 months of pregnancy. Amniocentesis & Chorionic villus sampling are also pregnancy testing procedures.


Dr. Ahmed Zayed

Dr. Ahmed Zayed Helmy holds a baccalaureate of Medicine and Surgery. He has completed his degree in 2011 at the University of Alexandri

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