By Andrea Rodrigo BSc, MSc (embryologist).
Last Update: 02/02/2018

A cryptic pregnancy, also known as undetected pregnancy, stealth pregnancy or hidden pregnancy, is a condition in which a woman is pregnant without knowing it, as there’s no hCG detectable in her system. As a consequence, she cannot get medical confirmation due to negative home pregnancy tests and hCG blood tests. The fetus may go undetected by her and the doctors, even until delivery.

Cryptic pregnancy is related to hormonal imbalances, and the most common causes are PCOS, recent pregnancy, early menopause, breastfeeding, birth control, high-stress levels, and very low body fat. The symptoms associated are “odd” periods, typical pregnancy symptoms, and negative ultrasounds. The length of a cryptic pregnancy is longer, as the fetus grows slowly due to the lack of hCG in the body.

Definition

A cryptic pregnancy, stealth pregnancy or undetected pregnancy is a rare phenomenon where the woman does not know she is pregnant until she reaches 20 weeks of pregnancy or more, or even until she reaches labor. Medical confirmation is not possible due to a lack in the production of human chorionic gonadotropin (hCG) by the body.

Cryptic or stealth pregnancy is considered a pathology of pregnancy and is medically considered a type of pregnancy denial.

It often occurs to women who have been on birth control methods, including the contraceptive pill of even tubal ligation. They can experience common pregnancy symptoms, such as fatigue or morning sickness, or nothing at all. They are, however, mistaken as those of some other condition.

The length of a cryptic pregnancy can range between 3 and even 5 or 7 years, due to slow growth of the fetus as a consequence of low hCG levels. Fetal development is delayed and interrupted very often, although this does not necessarily affect the health of the future baby.

The incidence rate of this condition is 1:475. Statistically, it is estimated that about one in 450 women who are pregnant don’t even know they are so until they reach the 20th week of pregnancy, and one in 2,500 don’t become aware until they reach labor.

Causes

A cryptic pregnancy occurs as a consequence of hormonal imbalances, which can be caused by any of the following reasons:

Polycystic Ovary Syndrome (PCOS)
It leads to the formation of small cysts on the ovaries, which become enlarged. This causes hormonal imbalances in the woman’s body.
Low body fat
It typically happens in female athletes. Having low body fat can trigger a hormonal imbalance.
Early menopause or perimenopause
The body starts showing signs of menopause as early as in the 30s. This causes the pregnancy to go unnoticed, as its symptoms are associated with those of perimenopause.
Recent pregnancy
After a pregnancy, your hormones need some time to get back to their normal levels. If you get pregnant again too early, or even while breastfeeding, there can be a hormonal imbalance.
Birth control methods
Especially Deprovera, Mirena coil, and Norplant. They release hormones that can affect normal pregnancy hormones.
Stress
High stress levels can affect a woman’s hormones to the point of causing a cryptic pregnancy.

Although pregnancy tests are negative, your belly continues growing slowly. Given that you cannot get medical confirmation of pregnancy, your doctor may think you have irritable bowel syndrome (IBS) and recommend that you stop eating gluten and sugar.

Symptoms

The symptoms of a cryptic pregnancy are similar to a regular pregnancy, although often milder. However, as in normal pregnancies, the symptoms vary from woman to woman, and some may have no symptoms at all. The most common include:

  • Odd periods
  • Nausea
  • Fatigue
  • Vomiting
  • Food aversions
  • Frequent urination
  • Weight gain
  • Headaches
  • Heartburn
  • Abdominal cramps
  • Metallic taste in the mouth
  • Back pain
  • Slow belly growth

You may feel fetal movement at some point, although it is often confused with gas, bloating, constipation, and/or muscle spams. Also, you may continue getting your regular periods in the form of light or spot bleeding with clots.

Having continued periods or bleeding in a cryptic pregnancy is not an indicator of miscarriage. It is due to the lack of hCG production or the small amounts of hCG in the body.

Detection

In a cryptic pregnancy, the result of pregnancy tests is negative because the levels of hCG are too low to be detectable. There’s hCG secretion by the placenta, but its levels are too low that the lining of the uterus (endometrium) sheds each month, which doesn’t allow hCG to build up and show up in pregnancy tests.

Also, in most cryptic pregnancy cases, ultrasound scans cannot detect the growing fetus. Certain uterine malformations or abnormalities can promote this situation, including:

Retroverted, tipped or tilted uterus
The uterus is inclined towards the back of the pelvis.
Bicornuate uterus
The uterus has two “horns” and looks heart-shaped.
Uterine scarring
As a consequence of C-section, tummy tucks, abdominal surgery, etc. It prevents the ultrasound waves from passing into the womb.

The good news is that, in most cases, cryptic pregnancies can be detected after the 20th week of pregnancy, since the weight gain and the presence of pregnancy symptoms become more obvious. In other cases, unfortunately, cryptic pregnancy lasts for the entire term and is detected when the woman goes into labor and begins experiencing uterine contractions.

Complications & prevention

The fact that the woman is pregnant without knowing it leads to a lack of prenatal care. As a consequence, the mother may not avoid certain toxic habits such as smoking, drinking, taking street drugs, doing vigorous activities, etc.

Also, it can cause prenatal complications such as hypertension, diabetes, or blood group incompatibility. If untreated or not treated on time, these complications can put both the mother and the baby at risk.

If you are on your reproductive age and continuously experiencing strange symptoms like certain pain or changes in your abdomen or pelvis, we recommend that you see your doctor as soon as possible. Although it is difficult to detect, he or she might make a guess about it.

Labor

More often than not, the delivery in cases of cryptic pregnancy turns out to be at home or unassisted, as it occurs suddenly. The labor pains will initially seem like menstrual cramps before you enter into labor.

In cryptic pregnancies, the labor pains can be experienced for months before entering into actual labor. This helps to confirm the pregnancy in time, as they prompt the woman to see a doctor. He or she may induce labor or perform a C-section.

Labor in cryptic pregnancies comes with a series of symptoms that can help you suspect that you’re indeed pregnant:

  • Nausea and/or vomiting
  • Back pain
  • Hot flashes
  • Shivering
  • Dizziness and/or blurred vision
  • Cold sweats
  • Mood swings
  • Pain in the legs, hip and/or pelvic region
  • Palpitations
  • Vagina feeling bruised, painful and swollen
  • Painful breasts
  • Pressure on the cervix

In some cases, the delivery process is quick and not so painful, mainly due to a lack of preparation for the birth. That is why some doctors recommend an emergency delivery or a C-section in cases of cryptic pregnancy.

FAQs from users

Can you be pregnant and miscarry without knowing it?

By Andrea Rodrigo BSc, MSc (embryologist).

Yes, it is a type of miscarriage known as blighted ovum or anembryonic pregnancy, in which the pregnancy loss occurs so early that the woman was still unaware that she was pregnant. It can occur in cryptic pregnancies as well. Read: What Causes a Blighted Ovum? – Symptoms, Diagnosis & Treatment.

Can you get pregnant on the pill and not know it?

By Andrea Rodrigo BSc, MSc (embryologist).

Yes, in fact, birth control pills are one of the causes that lead to cryptic pregnancy. No contraceptive is foolproof, and the pill is no different.

Will I experience baby movement despite going through a cryptic pregnancy?

By Andrea Rodrigo BSc, MSc (embryologist).

Yes, but you’re likely to confuse it with gas or irritable bowel syndrome (IBS) symptoms. When the baby is moving or kicking, you interpret it as muscle spams, fibroids, cysts or even intestinal worms.

Suggested for you

Throughout this post, we have made numerous references to the hCG hormone, that is, the pregnancy hormone. What do you know about? We recommend that you visit the following post to learn more about it: What Are Normal hCG Hormone Levels during Pregnancy?

There exist other strange pathologies that can cause “mystery” pregnancies. If you are curious and want to learn more about them, these are the most common ones:

Finally, the following guide will teach you what are the normal stages of pregnancy and how does fetal development occur in normal, 9-month pregnancies. All you have to do is click here: Pregnancy Stages by Month – Fetal Development with Pictures.

Authors and contributors

 Andrea Rodrigo
BSc, MSc
Embryologist
Bachelor's Degree in Biotechnology from the Polytechnic University of Valencia. Master's Degree in Biotechnology of Human Assisted Reproduction from the University of Valencia along with the Valencian Infertility Institute (IVI). Postgraduate course in Medical Genetics. More information