You took a beta hCG yesterday and the number came back lower than you expected. Or you are reading ahead, trying to understand what could have caused a low number. Within an hour of searching you have read that your morning coffee, your DoorDash sushi, the wine you had before you knew, your gym session, and last weekend's hot bath are all suspect. This post is the doctor answer to which of those actually matters.
What causes low hCG levels in early pregnancy
Most "low" beta hCG values are not actually low. They are earlier-than-expected dates. You ovulated later than the calendar predicted, or the embryo implanted later than typical. The number for your actual gestational age is normal. The number for the gestational age you thought you were at is low. The clinician interpreting the result will adjust the expected range to your trigger date, transfer date, or LMP1.
When hCG is genuinely low and not rising at the expected pace, the causes fall into a short clinical list.
Nonviable intrauterine pregnancy: a pregnancy with a chromosomal abnormality, which is the leading cause of first-trimester loss, often produces hCG that rises slowly or plateaus and then falls2. This is not caused by anything the patient did before or after the positive test.
Ectopic pregnancy: a pregnancy implanted outside the uterine cavity often produces hCG that rises slowly, by less than the Barnhart-defined 53 percent over 48 hours1,5. Ectopic pregnancy presents with a low or slow-rising beta, with or without one-sided pain or spotting, and is one of the reasons your clinic monitors beta trends rather than single numbers.
Very early pregnancy: the number is not low for what it is. You tested too early. The next beta in 48 hours will clarify whether the rise is normal or not.
These are the genuine causes. The list of things that do not cause low hCG in early pregnancy is much longer than the list of things that do, and it includes almost everything the internet will flag when you search for an explanation.
Caffeine does not cause low hCG. Moderate exercise does not. Sex does not. Hair dye does not. Mild stress does not. Your prenatal vitamins do not. The cold medication you took before you knew does not. The wine you had at a wedding before the test was positive does not. None of those, in isolation or in combination, cause low hCG in early pregnancy.
The same logic applies to the "did I cause my loss" question that comes after a difficult result. The honest clinical answer is: almost certainly not. First-trimester losses are overwhelmingly driven by chromosomal abnormalities present at conception, not by lifestyle factors in the days or weeks after implantation2,3.
What is actually unsafe in early pregnancy
There is a short list worth memorising. Most of it is uncontroversial, and most of it is shorter than the list pregnancy apps imply.
Smoking, including vaping: increases risk of miscarriage, ectopic pregnancy, low birth weight, and preterm birth. Stop once you know.
Alcohol once the test is positive: no safe amount has been established in pregnancy. The pre-positive exposure question is covered below; from the positive test onward, the recommendation is to stop3,5.
Recreational drugs, including cannabis: avoid all.
Untreated symptomatic UTI, bacterial vaginosis, or STI: treat promptly. Untreated genitourinary infection raises preterm birth risk5.
High-mercury fish: shark, swordfish, king mackerel, tilefish, and bigeye tuna. Mercury accumulates in the central nervous system and crosses the placenta. Most other fish, including salmon, sardines, light tinned tuna in moderation, and most freshwater fish, are safe and a useful source of omega-3s4.
Listeria-risk foods: unpasteurised soft cheeses, raw milk, deli meats not heated to steaming, refrigerated smoked seafood, pre-prepared deli salads. Listeria is rare but disproportionately dangerous in pregnancy4.
Raw or undercooked meat, fish, and eggs: bacterial and parasitic risk. Cook to safe internal temperatures.
Core body temperature elevation in the first trimester: hot tubs and saunas above 39°C (102°F), prolonged hot baths, fever above 38°C (100.4°F). Sustained core temperature elevation in early pregnancy is associated with an increased risk of neural tube defects. Brief warm showers and normal climate exposure are fine.
Specific medications: isotretinoin, methotrexate, some anti-epileptics, ACE inhibitors, warfarin, and several specific antibiotics. Check every prescription medication with your reproductive endocrinologist (RE) or OB. The MotherToBaby fact sheets (from the Organization of Teratology Information Specialists) are the most reliable source for medication-by-medication evidence6.
Cat litter without hand washing: toxoplasmosis risk. Wear gloves if you handle litter, and wash hands afterwards.
Contact sports, high-fall-risk activities, lifting injurious loads: sensible avoidance through the first trimester.
What is safe, despite what the internet says
This list contradicts a lot of forum advice. The evidence base for each item is solid.
Caffeine, up to 200 mg per day: the ACOG threshold is 200 mg/day across pregnancy1. That is one regular brewed coffee, or two small cups, or several cups of tea. Decaf is unlimited. The "no caffeine at all" rule is more conservative than the evidence requires.
Sex: safe in a normal pregnancy. The cervix and amniotic sac protect the pregnancy. Avoid if your clinician has flagged placenta previa, after preterm rupture of membranes, or if you have unexplained bleeding.
Exercise: approximately 150 minutes per week of moderate-intensity activity is recommended in pregnancy2. Pre-pregnancy activity levels can usually continue. Walking, swimming, prenatal yoga, light strength training, and most cardio you were doing before the pregnancy are safe. The exceptions are contact sports, activities with significant fall risk, and scuba diving.
Hair dye, manicures, pedicures: limited evidence of risk. Most OB practices allow them. Switching to ammonia-free dye in the first trimester is a conservative choice but not required by evidence. Well-ventilated salons are safe.
Travel: safe in the first trimester with a normal pregnancy. Hydrate. Walk every 1 to 2 hours on long flights to reduce DVT risk. Most airlines allow travel through week 36 without restriction.
Common over-the-counter medications: paracetamol (acetaminophen) for pain. Most antacids (Tums, Gaviscon). Stool softeners. Prenatal vitamins. Always cross-check with your provider, but these are the standard safe baseline3.
Most herbal teas in normal kitchen quantities: ginger tea for nausea, peppermint, rooibos, most fruit teas are fine. Concentrated herbal supplements, particularly anything marketed for "uterine toning" or hormonal effect, should be reviewed with your provider before use.
The "before you knew" guilt
This is one of the most common conversations I have in the first month after a positive test in pregnancy after infertility. The reader has read forum threads about exposures that "must have caused" outcomes and is now mentally cataloguing every glass of wine, every hot bath, every Advil they took in the weeks before the positive test.
The clinical answer is reassuring. From fertilisation until about day 12 to 14 post-ovulation (the period that overlaps with the missed period and the first positive test), the embryo operates in what is sometimes called the "all or nothing" period3,5. Either an exposure is severe enough to end the pregnancy at this stage, in which case the period arrives and the pregnancy is not detected, or the embryo continues largely unaffected. The single glass of wine at a wedding, the one round of high-impact exercise, the hot bath before you knew, the Advil for a headache: none of these, in the overwhelming majority of cases, cause loss or birth defects when they occurred before or around implantation.
This is not permission to keep doing those things now that you know. It is permission to stop carrying guilt for the time before. The most useful action you can take about pre-positive exposures is to change behaviour going forward, not to relitigate the past.
What if I am not sure about a specific exposure
The single most useful resource is the MotherToBaby fact sheet library (Organization of Teratology Information Specialists)6. It covers most specific exposures, medications, and substances with current evidence and is updated regularly. The fact sheets are written for both clinicians and patients.
For specific medications, your prescribing clinician's review beats forum advice. The question "did this medication I took yesterday matter" is exactly what your RE or OB expects you to ask, and the answer is rarely the catastrophic one the search results imply.
When in doubt, call. The threshold for calling the clinic about an exposure is lower than the threshold for calling about bleeding or pain. Most clinics field these calls daily.
Pregnancy after fertility treatment: a few extras to know
Continue progesterone, low-dose aspirin (81 mg), metformin, and thyroid medication exactly as prescribed unless your RE specifically instructs otherwise7. Stopping these on your own is one of the most common avoidable causes of unnecessary scares in the first 48 hours after a positive test.
Do not restart pre-pregnancy supplements you paused for the cycle without checking. Some "wellness" supplements, particularly high-dose vitamin A (retinol), certain "fertility blend" formulas, and some herbal preparations, are unsafe in pregnancy. Bring your full supplement list to the first appointment.
Hot flashes from PIO or progesterone supplementation feel like fever. They are not the same as fever. They do not raise your core body temperature dangerously and they do not require any action other than the cool drink and the fan you were going to reach for anyway.
What is normal, what is not
Reassuring: occasional caffeine within the 200 mg threshold, normal exercise, sex in a normal pregnancy, mild over-the-counter medication for a clear indication, and following your RE's medication taper schedule.
Yellow flag, worth a phone call but not an emergency: a new symptom that does not fit your pattern, fever above 38°C, persistent vomiting with poor fluid intake, light bleeding without severe pain, exposure to a medication you are unsure about.
Red flag, same-day clinic contact: heavy bleeding with severe cramping, severe one-sided pelvic pain, shoulder-tip pain, dizziness, fainting, signs of significant infection.
What to do (and not do) this week
Do write down everything you are taking. Prescriptions, OTC medications, supplements, vitamins. Bring the list to the next clinic visit. This is the single most useful piece of preparation for the OB intake.
Do keep moving. Sedentary first trimesters do not improve outcomes.
Do hydrate. Dehydration mimics and worsens nausea.
Do not spiral on a single pre-positive exposure. The math of teratology does not work the way the math of guilt does.
Do not take advice from a Facebook group about whether to stop a medication. Call the prescriber. The question of what causes low hCG levels in early pregnancy has a short clinical list, and almost nothing on it is something you did or did not do this week.
What's next
- For the symptom calibration that pairs with this post, see first trimester symptoms: what's normal week by week.
- For specific beta hCG number anxieties, see low beta hCG: when to worry and beta hCG numbers by week.
- For the wait between scans and the surveillance pattern in PAI, see PAI anxiety milestones.
- For the handoff to OB at the end of the first trimester, see graduating from your RE to an OB.
Sources
- American College of Obstetricians and Gynecologists. Committee Opinion No. 462: Moderate Caffeine Consumption During Pregnancy. Obstetrics & Gynecology 2010;116(2 Pt 1):467-468 (reaffirmed). Link
- American College of Obstetricians and Gynecologists. Committee Opinion No. 804: Physical Activity and Exercise During Pregnancy and the Postpartum Period. Obstetrics & Gynecology 2020;135(4):e178-e188. Link
- American College of Obstetricians and Gynecologists. Practice Bulletin No. 189: Nausea and Vomiting of Pregnancy. Obstetrics & Gynecology 2018;131(1):e15-e30. Link
- Centers for Disease Control and Prevention. Listeria and Pregnancy: People at Risk. CDC public health guidance. Link
- National Institute for Health and Care Excellence. NG201: Antenatal care. 2021. Link
- Organization of Teratology Information Specialists (OTIS). MotherToBaby Fact Sheets. Link
- American College of Obstetricians and Gynecologists. Committee Opinion No. 743: Low-Dose Aspirin Use During Pregnancy. Obstetrics & Gynecology 2018;132(1):e44-e52. Link
Common questions
Does caffeine cause low hCG in early pregnancy?
No. Caffeine does not cause low hCG, and neither does moderate exercise, sex, hair dye, mild stress, prenatal vitamins, or cold medication taken before you knew. When hCG is genuinely low, the causes fall into a short clinical list: a nonviable intrauterine pregnancy, an ectopic pregnancy, or a pregnancy that is simply earlier than expected. None of these are caused by what you did before or after the positive test.
How much caffeine is safe in pregnancy?
The ACOG threshold is 200 mg per day across pregnancy. That works out to roughly one regular brewed coffee, two small cups, or several cups of tea, and decaf is unlimited. The "no caffeine at all" rule is more conservative than the evidence requires.
Could the wine or hot bath I had before I knew I was pregnant have caused harm?
In the overwhelming majority of cases, no. From fertilisation until about day 12 to 14 post-ovulation, the embryo is in what is sometimes called the "all or nothing" period: an exposure is either severe enough to end the pregnancy before it is detected, or the embryo continues largely unaffected. A single glass of wine, one hot bath, or an Advil for a headache before the positive test does not, in most cases, cause loss or birth defects.
Is exercise safe in the first trimester?
Yes. Approximately 150 minutes per week of moderate-intensity activity is recommended in pregnancy, and pre-pregnancy activity levels can usually continue. Walking, swimming, prenatal yoga, light strength training, and most cardio you were already doing are safe. The exceptions are contact sports, activities with significant fall risk, and scuba diving.
Should I stop my fertility medications after a positive pregnancy test?
No. Continue progesterone, low-dose aspirin (81 mg), metformin, and thyroid medication exactly as prescribed unless your RE specifically instructs otherwise. Stopping these on your own is one of the most common avoidable causes of unnecessary scares in the first 48 hours after a positive test. Call the prescriber before changing any medication rather than acting on forum advice.