Search our site

Custom Search

Sunday 12 January 2020

Silent Miscarriage (Things We Don’t Know about Pregnancy Series #11)

Miscarriage is a common medical complication that leads to the loss of a pregnancy before 23 weeks, and affects one in four women during their reproductive lifetime. Depending on how early or late it happens, it can have bigger or smaller impacts on a woman’s physical and mental health.

But why does it happen? Is it mostly to do with lifestyle, or genetics? Is there something you can do to prevent it? And how can we get early warnings of silent miscarriages – the ones you never even knew had happened?

If you’ve ever been pregnant – miscarriage or not – you’ll probably have wondered about these things, and worried about them, as I have. Whilst the chance of miscarriage drops off rapidly with time, stillbirth and postnatal foetal death are still classed as late pregnancy losses, and do happen from time to time, meaning there is no good time to truly forget about it.

Chances of miscarriage drop as pregnancy progresses. © TWDK. Data from:

Most miscarriages make themselves evident with symptoms including abdominal pain, discharge, and vaginal bleeding. These symptoms can abate, or progress to the expulsion of the foetal tissue after days or even weeks. However, once it’s started, we don’t know any way to stop it: nature simply runs its course. Sometimes the uterus doesn’t empty out properly, and an operation has to be performed called dilatation of the cervix and curettage of the uterus (or D & C) – but most women still know about it.

There are five main reasons for a miscarriage: (i) genetic or chromosomal abnormalities, (ii) health and lifestyle factors, (iii) health conditions, (iv) mis-implantation, or (v) placental problems.

(i) Sometimes a foetus inherits a faulty gene, or copying errors occur when cells are dividing early on. This can lead to birth defects and health problems or a miscarriage – accounting for about 50% of miscarriages[1]. Genetic or chromosomal abnormalities are more common for older parents.
DNA © ynse (CC BY-SA 2.0)
(ii) Lifestyle factors such as smoking, drinking, obesity, or malnutrition, can sometimes lead to miscarriage. Exercise, however, is not a risk factor. To find out more about exercising whilst pregnant, read our earlier blog post on the topic.
(iii) Health conditions like uncontrolled diabetes, thyroid disease, high blood pressure, food poisoning, infections (especially in the uterus), trauma, or hormonal disorders, can directly lead to miscarriage, or their treatments might: some medications, for example, may be incompatible with pregnancy and spontaneously abort a growing foetus, perhaps even before the mother knows she is carrying.
(iv) On occasion, an egg implants outside the uterus (usually on the walls of the fallopian tube). This is an ectopic pregnancy, and a medical emergency. Ectopic pregnancies are always unviable – we don't know how to 'fix' them.
After the fertilisation of an egg, hormones are produced that mean a woman can test as pregnant. These hormones drive the development of the placenta. As the placenta forms, it develops a complex network of blood vessels between the mother’s tissues and the baby’s – and when it comes away at birth, these are severed. The uterus is built to deal with this, but other parts of the body are not, and a placenta growing in the wrong place can lead to massive internal bleeds. Because of this growth it can’t be taken out and put back in in the right place, it has to be surgically removed. Ectopic pregnancies usually make themselves known through bleeding, cramping, dizziness, and vomiting, or pain in the shoulder. Around 1 in 80-90 pregnancies are ectopic in the UK.
Uterus. Image via Wikipedia Commons.

(v) Several things can affect the healthy development of the placenta, from blood disorders to multiple pregnancies, substance misuse to trauma, and several ways a placenta can malfunction, including insufficiency (not passing the baby enough nutrients), abruption (coming off the uterus wall too early), previa (where it blocks the cervix and gets in the way of birth), or accreta (where it won’t come off). Placental abruption in particular is linked to miscarriage, although there are other ways it can malfunction: the placenta is a bit of a mystery and medical researchers are still looking into it. To find out more about the placenta, read our earlier blog post on the topic.

Silent or “missed” miscarriages

Perhaps the scariest kind of miscarriage is the kind you didn’t know about. They may not take the same physical toll, but it’s easier for them to go longer undetected.

Sometimes if a miscarriage happens early enough in pregnancy, the woman may not know she’s pregnant and mistake the miscarriage for a late period. These miscarriages are known as chemical pregnancies because they progress far enough to register a positive pregnancy test, but no further.

Other times, the baby has died but stayed in the uterus. This is known as a ‘missed miscarriage’. There can be no symptoms at all, or the only symptoms are loss of pregnancy symptoms. Since symptoms naturally come and go, especially early on, silent miscarriage diagnosis is difficult and stressful.

Molar pregnancies

Molar pregnancy. Image via Wikipedia Commons.
Molar pregnancies look like a bundle of fish eggs blocking up the uterus. Most women don’t know about them until they have their 12 week scan, as normal pregnancy symptoms progress. No one knows why they happen, but they have to be surgically removed – occasionally by full hysterectomy. For a molar pregnancy to happen, there must something wrong with the fertilised egg, such as missing a nucleus – but not all non-viable eggs lead to molar pregnancies.

If it doesn’t lead to a miscarriage, a molar pregnancy can grow deeper into the uterine tissues and spread. This is known as an “invasive mole”, and in 2-4% of cases develops into cancer. Younger (under 20) or older (over 35) women are more likely to suffer molar pregnancies, women who suffer nutritional deficiencies of protein, folic acid, or carotene, or women who’ve had a molar pregnancy before – we don’t know why.

Blighted ovum


A blighted ovum or anembryonic pregnancy happens when the sac for the baby develops without a baby in it. Again, normal pregnancy symptoms progress, and it usually takes the 12-week scan to uncover the awful truth. The sac has to be removed surgically.

The empty sac means that the fertilised egg never implanted, or didn’t develop properly, and instead got reabsorbed back into the uterus. Whilst this happens early on, if the placenta continues growing, it makes all the hormones associated with pregnancy anyway, masking the loss. Scientists don’t know what causes a blighted ovum, but it could be linked to complications chromosome 9 and is more common if the parents are biologically related.

Following late miscarriages, foetal DNA is tested to explore potential genetic causes. There are also various ongoing research projects looking into miscarriage, including identifying risk factors, trialling stem cells to see if they can mitigate against recurrent miscarriage, and investigating the links between heart and blood vessels and miscarriage. Many researchers think that miscarriages may be preventable.

There are many unknowns when it comes to pregnancy, and over the next few months, I’ll be exploring more of them with you. Look out for my next blog post, which will be about determining the sex of a baby

Check out our full article on the things we don't know about pregnancy. This article will be updated as we add posts across the coming months.

why don't all references have links?

[1] van den Berg, Merel MJ, et al. Genetics of early miscarriage. Biochimica et Biophysica Acta (BBA)-Molecular Basis of Disease 1822.12 (2012): 1951-1959.

No comments:

Post a Comment