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Early Pregnancy

Including HCG levels and ultrasound findings

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Background

When pregnancy begins depends on how "pregnancy' is defined.

Does pregnancy begin when the sperm first penetrates the egg?

Does it begin when the male and female pronuclei containing the chromosomal material move close together and decondense within the newly fertilized egg?

A human embryos several hours after fertilization
The 2 circles (pronuclei) in the center contain the maternal and paternal DNA
The sperm and egg were put together 16 hours prior to this photo

Embryo Images

Does it begin when the male and female chromosomes pair up with each other and the fertilized egg subsequently divides into a 2-cell embryo?

Does it begin when the embryo begins implantation about 6 days after ovulation?

Or, does it begin when the woman recognizes that she is pregnant after her missed menstrual period and positive pregnancy test?

HCG levels in pregnancy

HCG, or human chorionic gonadotropin, is a hormone made by the pregnancy that can be detected in the mother's blood or urine even before the woman's missed period. This hormone is what we look for with a "pregnancy test".

HCG is first detectable in the blood as early as 7-8 days after ovulation by very sensitive HCG assays (research assays). In real life, blood pregnancy tests will be positive (> 2 mIU/ml) by 10-11 days after HCG injection or LH surge.

In general, the HCG level will double every 2-3 days in early pregnancy.

85% of normal pregnancies will have the HCG level double every 72 hours.

HCG levels peak at about 8-10 weeks of pregnancy and then decline, remaining at lower levels for the rest of the pregnancy.

There is a large variation in a "normal" HCG level for any given time in pregnancy.

Pregnancies destined to miscarry or to be ectopic (tubal) pregnancies tend to show lower levels (eventually), but often have normal levels initially.

Some normal pregnancies will have quite low levels of HCG - and deliver perfect babies. Caution must be used in making too much of HCG "numbers". Ultrasound findings after 5-6 weeks of pregnancy are much more predictive of pregnancy outcome than are HCG levels.

For women that have had an HCG injection as part of their infertility treatment, the hormone will take about 5-14 days to clear from the woman's system, depending on the dose and the individual woman. This can causes problems with interpretation of pregnancy tests done earlier than 14 days after an HCG injection.

HCG levels from normal singleton pregnancies

Levels are listed for various days after the ovulatory HCG injection or LH surge
First (same as Third) International Reference Preparation was used (Second IRP gives lower values)
"High" is highest seen in this group of pregnancies
"Low" is lowest seen in this group of pregnancies
"#" is the number of tests done for that day in this group of pregnancies

These values are from a group of 53 normal singleton pregnancies (a very small group)
Because this is a very small group of patients and because lab assays vary, it is important not to rely on these values to try to determine whether your pregnancy is viable, single, twin, etc.

Check with your physician about your own levels

NORMAL SINGLE PREGNANCIES

The information in the table above is part of a study carried out by Dr. Sherbahn that compared HCG levels from single, twin and heterotopic (combined intrauterine and ectopic) pregnancies.

HCG levels from normal twin pregnancies

Twin pregnancies tend to show higher HCG levels on a given day of pregnancy. However, there is a large variation in HCG levels between pregnancies, and much overlap exists between single and twin pregnancies.

Levels are listed for various days after the ovulatory HCG injection or LH surge
First (same as Third) International Reference Preparation was used (Second IRP gives different values)
"High" is highest seen in this group of pregnancies
"Low" is lowest seen in this group of pregnancies
"#" is the number of tests done for that day in this group of pregnancies

These values are from a group of 29 normal twin pregnancies (a small group)
Because this is a very small group of patients and because lab assays vary, it is important not to rely on these values to try to determine whether your pregnancy is viable, single, twin, etc.

Check with your physician about your own levels

NORMAL TWIN PREGNANCIES

The information in the table above is part of a study carried out by Dr. Sherbahn that compared HCG levels from single, twin and heterotopic (combined intrauterine and ectopic) pregnancies.

Ultrasound in early pregnancy

Select the images you would like to view::

Transvaginal ultrasounds of normal pregnancies at 5.5 weeks of gestation

Gestational sac (black area) is seen with yolk sac inside

An identical (monozygotic) twin pregnancy at the same stage is shown as well as an early twin pregnancy showing non-identical (fraternal) twins

Transvaginal ultrasound of a normal pregnancy at 6.5 weeks of gestation

The same pregnancy as shown above - exactly 1 week later
Fetus is between white cursors, and is 3 mm long

Transvaginal ultrasound of a normal pregnancy at 8.5 weeks of gestation

Same pregnancy 2 weeks later
Fetus is now 19 mm long (3/4 inch)
A "head" area and a body area are now distinguishable

Transvaginal ultrasound of a normal pregnancy at 12 weeks of gestation

This fetus is 51mm long (2 inches)