Miscarriage Causes and Risks: An Evidence-Based Guide

• Miscarriage is common — about 15–20% of clinically recognised pregnancies end in loss, and the true figure including very early losses is closer to 1 in 3 conceptions.
• The leading cause of early miscarriage is a random chromosomal error in the embryo — present from before you knew you were pregnant and not caused by anything you did.
• Maternal age is the single strongest non-modifiable risk factor, because egg quality declines with age.
• Some risks are modifiable: uncontrolled diabetes or thyroid disease, smoking, severe obesity or underweight, and certain infections — all can be addressed before pregnancy.
• Foods like papaya, normal exercise, sex, stairs, lifting, and everyday stress do NOT cause miscarriage. Self-blame is almost always misplaced.
• Workup for recurrent loss is recommended after two or more miscarriages — and most women who miscarry once go on to have a healthy pregnancy.

• Threatened miscarriage — bleeding in early pregnancy with a closed cervix and a viable baby on scan. Many of these settle and the pregnancy continues normally.
• Inevitable miscarriage — bleeding with an open cervix as the pregnancy is being passed.
• Incomplete miscarriage — some pregnancy tissue has passed but some remains, sometimes needing further treatment.
• Complete miscarriage — all tissue has passed and the uterus is empty on scan.
• Missed miscarriage — the baby has stopped developing but there are no symptoms; it is found at a routine scan.
• Anembryonic pregnancy (blighted ovum) — a pregnancy sac forms without an embryo, accounting for around 30–50% of first-trimester losses.
• Recurrent miscarriage — two or more losses (modern ESHRE/RCOG definition); investigation is recommended after two.

By a wide margin, the commonest cause of first-trimester miscarriage is a chromosomal abnormality in the embryo that is incompatible with continued development. When tissue from miscarriages is tested, around 50–75% of first-trimester losses carry an abnormal chromosome pattern — and that figure rises further with more sensitive testing such as microarray.

Most of these are aneuploidies — the embryo has the wrong number of chromosomes. They include trisomies (an extra chromosome, with trisomy 16 the single most common in miscarriage), monosomy X (Turner syndrome), and triploidy. These errors happen by chance during the formation of the egg or sperm, at fertilisation, or in the first few cell divisions. They are overwhelmingly random events, not the result of anything either parent did.

The single factor that most influences this rate is the age of the egg. Because all of a woman's eggs are formed before her own birth, the proportion carrying chromosomal errors climbs steadily with age — from roughly 10–15% of eggs in the twenties to 40% by 35 and 80–90% by the mid-forties. Sperm contributes too, and the risk rises modestly with paternal age over 45. A linked picture of how age shapes egg quality is covered in our guide for those trying to conceive after 30.

The takeaway is important and freeing: most miscarriages cannot be prevented by changing your behaviour, because the chromosomal error was already present before the pregnancy was even recognised. The body's passing of the pregnancy is a biologically appropriate response — not a failure on your part.

• Under 30: about 10%
• 30–34: about 12%
• 35–39: about 18%
• 40–44: about 33%
• 45 and over: 50% or higher

• Uncontrolled diabetes (type 1 or type 2): an HbA1c above ~7% can double the miscarriage rate or more. Aiming for HbA1c below 6.5% before conception is recommended. See diabetes in Indian women.
• Thyroid disease: overt hypo- or hyperthyroidism clearly raises risk, and anti-TPO antibody positivity is linked to loss even with a normal TSH. FOGSI suggests a TSH below 2.5 mIU/L when planning and during pregnancy — explained in thyroid and fertility.
• Antiphospholipid syndrome: a well-established cause of recurrent and late loss. It needs two positive antibody tests 12 weeks apart, and treatment with low-dose aspirin plus heparin markedly improves outcomes.
• PCOS: affecting 10–20% of Indian women of reproductive age and linked to higher loss rates, largely via insulin resistance. See PCOS and pregnancy.
• Weight extremes: both severe obesity (BMI over 35) and being significantly underweight (BMI under 18.5) raise risk.
• Other conditions: high prolactin, untreated celiac disease, lupus, severe kidney or heart disease, and poorly controlled chronic illness can all contribute.

A smaller but identifiable share of miscarriages — especially mid-trimester losses — are linked to the shape of the uterus, the cervix, or inherited chromosome rearrangements.

Uterine shape and lining. Congenital differences such as a septate uterus (a band of tissue dividing the cavity) are the most treatable structural cause; hysteroscopic removal of the septum can improve later outcomes. Acquired issues include intrauterine scarring (Asherman syndrome — often after a previous D&C or infection), submucosal fibroids distorting the cavity, and polyps. Diagnosis uses saline sonography, 3D ultrasound, hysteroscopy or MRI.

Cervix. Cervical insufficiency — painless opening of the cervix, usually in the second trimester — can cause mid-trimester loss; in selected cases a cervical cerclage (stitch) helps.

Parental chromosomes. In about 2–5% of couples with recurrent loss, one partner carries a balanced translocation. The carrier is usually perfectly healthy, but the embryo can inherit an unbalanced arrangement that ends in miscarriage. Parental karyotype testing is offered after two or more losses (roughly ₹4,000–₹8,000 per person), ideally alongside prenatal genetic counselling. In communities where consanguineous marriage is common, pre-conception genetic counselling and carrier screening are particularly worthwhile.

• Smoking — a clear, dose-dependent increase in risk; stopping before and during pregnancy is one of the most beneficial things you can do.
• Heavy alcohol — raises risk; abstinence is advised in pregnancy.
• Heavy caffeine (over ~300–400 mg/day, about 4 cups of coffee) — possibly a small increase; moderate intake under ~200 mg/day appears safe.
• Recreational drugs — substantially increase risk.
• Severe nutritional deficiency — low vitamin B12, folate and vitamin D may affect outcomes. Given how common low vitamin D and vitamin B12 are in India, sensible supplementation matters.
• Significant occupational exposures — heavy metals, ionising radiation, certain solvents — raise risk.

Infections cause a minority of miscarriages, but some are preventable or treatable. Bacterial vaginosis and ascending genital infections (chlamydia, gonorrhoea, trichomoniasis) have been linked to mid-trimester loss, and asymptomatic urinary infections should be screened and treated. Severe systemic illness — malaria, dengue, severe enteric fever, severe COVID-19, listeria from contaminated food — can end a pregnancy through high fever, low oxygen or direct effects.

In India, two infection issues deserve special mention. Genital tuberculosis, given the country's high TB burden, can damage the uterine lining and tubes and contribute to unexplained recurrent loss; it needs targeted testing and a full 6–9 month course of anti-TB treatment. And vector-borne and water-borne diseases (dengue, malaria, enteric fever, hepatitis A and E) peak in the monsoon and in endemic areas. Prevention helps: food and water hygiene, mosquito control, prompt treatment of fevers, and updating pregnancy vaccines (rubella and varicella before pregnancy; influenza and Tdap during it). Routine TORCH panel screening of women without symptoms is not recommended.

• Vaginal bleeding — from light spotting to heavy bleeding with clots. Light spotting in early pregnancy is common (20–30% of pregnancies, many of them normal) and does not always mean miscarriage.
• Cramping abdominal pain, pelvic pressure or low back pain — especially with bleeding — more strongly suggests an active miscarriage.
• Passage of tissue from the vagina.
• Loss of pregnancy symptoms (nausea, breast tenderness) may occur but is not specific.
• No symptoms at all — a missed miscarriage is often found only at a routine scan.

• Expectant management — letting the body pass the pregnancy naturally over days to weeks. It avoids medicines and surgery, costs little, and works in about 50–80% of cases within 2–6 weeks. It suits women with reliable access to emergency care who can tolerate uncertain timing.
• Medical management — misoprostol (in India as Cytolog or Misoprost, ~₹50–₹200), sometimes preceded by mifepristone, which lifts success rates to around 80–90%. Expect cramping, bleeding, nausea and sometimes fever; good pain relief and follow-up are essential.
• Surgical management — suction evacuation (preferred) or dilation and curettage (D&C), usually under sedation. It is quick, over 95% effective, allows tissue to be sent for genetic testing, and is the choice when there is heavy bleeding, infection, or when other methods have not worked. Costs typically range from ₹8,000–₹40,000.

• Heavy vaginal bleeding (soaking a pad an hour for two or more hours) or large clots.
• Severe or one-sided lower abdominal or pelvic pain.
• Shoulder-tip pain, fainting, severe dizziness or a racing heart — possible signs of ectopic pregnancy; go to an emergency department now.
• Fever, chills or foul-smelling vaginal discharge after a miscarriage — possible infection.
• Bleeding or cramping in early pregnancy, even if mild, so it can be assessed.
• Two or more miscarriages — ask for a recurrent-loss workup; do not wait for a third.
• Overwhelming grief, hopelessness or thoughts of self-harm — emotional care is part of recovery.

• Aim for a healthy weight (BMI 18.5–24.9 where possible).
• Get chronic conditions well controlled — diabetes (HbA1c below 6.5%) and thyroid (TSH below 2.5 mIU/L) especially.
• Stop smoking and limit alcohol.
• Start folic acid 400–800 mcg daily at least three months before conception (a higher 5 mg dose for selected high-risk women).
• Correct vitamin D and B12 deficiency, and review pregnancy supplements with your doctor.
• Update vaccines (rubella, varicella, hepatitis B, influenza, Tdap) before pregnancy.
• Book a pre-conception consult if you have had a previous loss, are older, or have a chronic condition.

• ACOG — Early Pregnancy Loss (Practice Bulletin)
• RCOG / NICE — Recurrent Miscarriage and Ectopic Pregnancy and Miscarriage Guidance
• NHS — Miscarriage: Causes
• ESHRE — Guideline on Recurrent Pregnancy Loss
• WHO — Maternal and Reproductive Health / Stillbirth Definitions
• FOGSI — Federation of Obstetric and Gynaecological Societies of India (clinical resources)