All the waiting comes to an end. The first visit to the gynecologist confirms the pregnancy. The doctor calculates the Expected Due Date (EDD). The excitement of being pregnant increases manifold with each passing day. Expectant mothers, especially first timers anxiously await their delivery day. In the midst of all these events, have you ever stopped to wonder how the doctor arrives at the magic date when you will hold your precious bundle for the first time.
EDD and LMP
Various methods of calculating the Expected Due Date (EDD) are prevalent. No one method is 100% fool proof. The probability of error increases in case of inaccurate recall of LMP by the mother, irregular mensuration, etc. Normally pregnancy due date or gestation period is calculated based on LMP (Last Menstrual Period).
Other methods of Calculating EDD
EDD can also be calculated using the Doppler ultrasound scan, Clinical examination, or the Human Chorionic Gonadotropin (HCG) pregnancy test.
Doppler Ultrasound Scan
By 10 to 12 weeks of fetal growth (10-12 weeks gestational age), the fetal heartbeat can be heard using Doppler ultrasound. (EDD can be calculated with this data.
HCG Pregnancy Test
HCG can be detected in the blood and urine of the expect ant mother between 6 to 14 days after fertilization (3-4 weeks gestational age)
Pelvic Examination along with accurate menstrual records in the first trimester is yet another method of pregnancy dating.
There exists a marginal chance of miscalculation because of the sheer number of variables to be considered. For instance, the fetus may grow at a different rate in individual cases. An expectant mother who gets appropriate rest and nourishment would have a better growth to her fetus as compared to an expectant mother who does not get either or both of the above. The number if variable factors to be considered are many.
To avoid this discrepancy, doctors use a couple of different EDD calculators in tandem. This normally results in a more accurate EDD. However, in cases where exact date of conception is known, due date of pregnancy can be calculated more accurately.
In vitro fertilization and EDD
Under normal circumstances it is difficult to know the exact date of conception. In vitro fertilization is one of the exceptions. Here, the date of conception is known and so EDD can be more accurately calculated. Assuming a cycle length of 28 days, add 266 days (36 weeks) to the date of conception to arrive at the EDD. The EDD will vary based on cycle length
Multiple pregnancy and EDD
In case of multiple pregnancies, which commonly occurs during in vitro fertilization, gestational age is calculated either based date of embryo transfer or using the larger fetus.
Regardless of the EDD, it is a good practice to keep a bag with all essentials packed for the hospital around the end of the 8th month of pregnancy. This should include your medical history, medications if any prescribed by your doctor and a few changes of clothes. Then just sit back and wait to hold your little bundle of joy!!