Early pregnancy symptoms can arrive quickly and feel unfamiliar, even if you have experienced premenstrual symptoms before. Deep tiredness, nausea at any hour, and breast tenderness that feels different from your usual premenstrual ache are among the most common, and all of them are your body responding to a fast hormonal shift that begins within days of conception. The first trimester covers the start of pregnancy through to the end of week 12.2
The hormones behind early pregnancy symptoms
Much of what you feel early on traces back to one hormone. Soon after conception, your body starts producing human chorionic gonadotropin (hCG), often called the pregnancy hormone. Its levels climb fast in early pregnancy, peaking at around nine weeks. That rapid rise drives a lot of the symptoms you feel in the first trimester, nausea included.3
Oestrogen and progesterone both climb steeply during early pregnancy. Progesterone softens the muscles of your womb so it can expand, keeps the pregnancy going until the placenta takes over, and relaxes the muscles of your digestive tract (which is part of why bloating and heartburn can creep in). At the same time, rising oestrogen works alongside progesterone to increase blood flow to the womb, support the growing uterine lining, and prompt structural changes throughout your body. Together, these hormonal shifts drive early physical symptoms while creating the environment your pregnancy needs to thrive.4
What is normal in the first trimester?
Nausea and vomiting, often called morning sickness, affect up to 80% of pregnant women. The name is misleading, because it can catch you at any time of day or night. It usually starts somewhere between weeks four and seven, and for most people eases by around 20 weeks.5
Other physical changes you may notice
Beyond nausea, plenty of other changes are typical in the first trimester:
- Tender, larger breasts
- Needing to wee more often
- Constipation
- Changes in vaginal discharge
- A metallic taste in the mouth
- A sharper sense of smell
- Food cravings and aversions6
Not noticing a particular symptom on this list does not signal a problem. Every pregnancy is different, and which symptoms show up, and how strongly, varies widely.
Where the pain tends to be in early pregnancy
Mild stomach cramps, sometimes described as period-like pains or growing pains, are common early on. They can come from ligaments stretching to support your growing womb, from constipation, or from trapped wind, and usually ease when you rest or change position. However, if the pain is severe, persistent, or accompanied by bleeding, seek medical advice promptly. Severe or prolonged pain in early pregnancy can be a sign of complications such as an ectopic pregnancy, a threatened miscarriage, or an ovarian cyst issue that needs urgent assessment.17
When to seek support
If you are being sick constantly and cannot keep any food or fluid down, call your GP or midwife. This can be a sign of hyperemesis gravidarum (HG), a severe form of pregnancy sickness that affects up to 3 in 100 pregnant women and sometimes needs hospital treatment. HG can start before 20 weeks and is different from typical morning sickness. If nausea and vomiting are wearing you down, your GP or midwife can offer support, reassurance, and advice on food and fluids. Where medication is needed, they may suggest antihistamines as a first option.8
Call your midwife, GP, or an early pregnancy unit if you have stomach pain alongside any of these:
- Vaginal bleeding or spotting
- Regular cramping
- Unusual vaginal discharge
- Pain when urinating
- Severe pain that does not ease with rest9