Cryptic Pregnancy - Negative Ultrasounds

Negative Ultrasounds

Ultrasounds can be negative even with a normal pregnancy, however, when the HCG test says there is a baby, typically the ultrasound technician will do everything that they can to find it. An overwhelming amount of ultrasounds in cryptic pregnancy are negative due to a number of reasons.

Retroverted uterus (tipped uterus)- Typically the uterus is tilted forward. However, about 1 in 5 women have a retroverted uterus. That is when the uterus is tilted toward the spine. There are several causes.

•   The uterus does not move to a forward position as the woman matures
•   The growing baby can stretch the ligaments holding the uterus in its place. If this happens, the uterus moves from its original position.
•   Past pregnancies that have stretched the ligaments
•   Fibroids or endometriosis cause scarring. This can cause the uterus to tip backward

In most cases, as the baby grows, the uterus straightens out, but in some cases it may not straighten. It depends on how severe the tilt is, and how it became tilted to begin with. One theory is that the uterus can be so tilted that the fetus grows under or behind the intestines, making a positive ultrasound almost impossible. This is not limited to early ultrasounds. There have been cases of negative ultrasounds performed very close to the time of delivery.

Incarcerated Uterus- The term incarcerated gravid uterus refers to a pregnant retroverted or retroflexed uterus that is entrapped in the pelvis between the sacral promontory and pubic symphysis. It has been reported to occur in 1 in 3000 pregnancies. The causes for an incarcerated uterus are:

Deep sacral concavity
Pelvic inflammatory disease
Endometriosis
Posterior wall leiomyoma
Didelphic uterus
Bicornuate uterus
Previous gynecologic surgery resulting in adhesions
Placental accreta

In most cases the retroverted uterus will eventually straighten out as it grows, but incarceration occurs when the fundus gets trapped under the sacral promontory. With the fundus trapped, the lower portion of the uterus then balloons toward the upper abdomen. This is known as sacculation. The cervix elongates and the bladder is pushed up. At the time of clinical examination, with advancing gestational age, the cervix and upper limits of the vagina cannot be reached at vaginal examination nor can the cervix be visualized. As the cervix and bladder stretch upward, they create a cavity echo, or a pocket of air, between it and the uterine wall.

***Ultrasound waves cannot travel through air. They are reflected back as an image of a void, and in the case of incarcerated uterus, especially with a cryptic pregnancy, they are misread and understood to be an empty uterus.

Bicornuate Uterus- Bicornuate uterus is a congenital abnormality of the uterus wherein it is heart-shaped, with two horns. A split uterus can be partial or complete, and it can affect the reproductive abilities of the woman, resulting in preterm birth and recurrent miscarriages. However, such women can also go on to have successful pregnancies without realizing that there is an abnormality in their uterus.

Abdominal Scar Tissue- If a woman has scar tissue due to abdominal surgery, tummy tuck or a previous C-section, it can prevent the ultrasound waves from reaching the uterus. The scar tissue can warp the uterus and create folds. As a result, the scan may be unable to pick up the growing baby. The ultrasound technician may not be able to see the fetus and will ultimately conclude that there is no pregnancy.