By Keith S. Wexler, MBA, Maternal Fetal Medicine, Prenatal Diagnosis and Biotech Consultant, GENASSIST, Inc.
Paul Wexler, M.D., F.A.C.O.G., Medical Director, GENASSIST, Inc.
Clinical Professor, Department of OB/GYN, University of Colorado Health Sciences Center
Clinical Professor, Division of Genetics/Dept. of Pediatrics, Univ. of Colorado/The Children’s Hospital
The ease and convenience of urine pregnancy test kits that are available across the counter may become positive as early as 6 days after fertilization.
This has allowed a woman to know that she is “pregnant” even before she misses a period. Once a woman knows that she has a positive pregnancy test, it can be confirmed with a maternal serum blood Beta HCG test.
We are getting calls from patients in their third or fourth week of pregnancy, many times even before they have seen their healthcare provider, to have a Viability Ultrasound.
Although patients are anxious to see the baby’s heartbeat so they can be reassured about the health of the pregnancy, a Viability Ultrasound is usually deferred until at least 5 weeks 3 days from a last menstrual period.
Often the heartbeat may not be visible until after 6 weeks gestation. Additionally, when a viability ultrasound is performed prior to 6 weeks gestation, a vaginal ultrasound is often the only way to confirm a heartbeat.
We have to weigh the patient’s anxiety and excitement against the technological limitations of the ultrasound equipment. We tell patients that even with Invitro Fertilization (IVF), when we know exactly when fertilization took place, we do not know exactly when implantation of the embryo took place.
Especially with infertility patients and multiple miscarriage patients, we usually want to wait until 6 1 / 2 weeks to 7 weeks gestation.
With all of the Non Invasive Prenatal Testing [NIPT] options available to the pregnant patient, more pressure is being placed on the healthcare provider to get a size and dates ultrasound early in pregnancy so that NIPT tests can be done as soon as possible.
Some offices are delaying seeing a patient until 10 to 12 weeks gestation, leaving many patients in early pregnancy uncertain about the welfare of the pregnancy.
Many insurance companies will only pay for two ultrasounds in pregnancy. Healthcare providers usually choose a First Trimester Aneuploidy Ultrasound at 11 to 14 weeks gestation and a second ultrasound (a Level II Ultrasound) at 18 to 22 weeks gestation.
Many insurance companies will NOT pay for a viability ultrasound unless there is a medical indication (e.g. bleeding in pregnancy).
A fetal heart may be seen with a transvaginal ultrasound when the fetal pole, usually seen attached to a yolk sac, measures greater than 2 mm.
- However, the fetal heart should be seen when the fetal pole measures 7 mm or greater.
- Usually the heart beat is greater than 100 beats per minute by 6.3 weeks gestation and greater than 110 to 119 beats per minute by 6.4 to 7 weeks gestation.
When discussing weeks of gestation, dates are calculated from the first day of the patient’s last menstrual period (LMP).
This is often confusing for patients since they are not pregnant on the first day of their LMP. The patient always expects that she is approximately 2 weeks less pregnant than the weeks gestation calculated by her healthcare provider which adds the approximately 2 weeks prior to ovulation when conception actually took place.
Patients talk about a pregnancy being 9 months long but medically a full term pregnancy is 40 weeks or 10 four week months from the LMP.
Occasionally a slow fetal heart rate (Fetal Bradycardia) will be detected early in pregnancy (e.g. less than 90 beats per minute before 6.3 weeks gestation from the LMP).
- Miscarriage rates appear to be increased in these cases (20% to 25%) compared with the miscarriage rate of only (5% to 10%) when fetal heart rates are in the normal range.
Some studies have suggested a possible increased risk for pregnancies with a slow fetal heart rate to have a slightly greater risk for a child with a chromosomal abnormality or heart defect whereas other studies have failed to show this relationship.
When a slower heart rate is detected in early pregnancy, the healthcare provider will often request a repeat ultrasound in 1-2 weeks to recheck the heart rate and ensure continued fetal viability. Additional testing may be recommended if the pregnancy continues.