What to Expect in Your First Trimester — A Complete Guide
Weeks 1 to 12 covered in full, for expectant parents in Bexley, Erith, Dartford and surrounding areas
Finding out you're pregnant is one of the most significant moments of your life. Whether you've been trying for a long time or it came as a complete surprise, those two lines on a test change everything — and the questions start almost immediately.
What's happening to my baby right now? Why do I feel so terrible? When do I tell people? What do I need to do first?
The first trimester — weeks one to twelve of pregnancy — is a period of extraordinary change. Your body is doing something remarkable, largely invisibly, and often while you're feeling at your worst. This guide covers everything you need to know about what's happening, what's normal, what to watch out for, and what to do during these first crucial weeks.
What Is the First Trimester?
The first trimester runs from the first day of your last menstrual period (LMP) to the end of week 12. In terms of actual conception, your baby is around two weeks younger than your pregnancy is dated — because pregnancy is counted from the last period rather than the moment of conception.
By the end of the first trimester, your baby is fully formed in miniature. All the major organs, limbs, and facial features are present. The remaining six months of pregnancy are primarily about growth and maturation rather than new structures forming — which is why the first trimester is considered the most critical period of development.
The risk of miscarriage is highest in the first trimester, which is why many people choose to wait until after twelve weeks to share their news widely. However, there is no rule about this — sharing earlier or later is entirely a personal decision.
Your Baby's Development Week by Week
Weeks 1 and 2 — Before Conception
In pregnancy dating, weeks one and two technically occur before conception. Week one is your period. Week two is when ovulation typically happens and conception occurs — usually around day 14 of a 28-day cycle, though this varies significantly between individuals.
Week 3 — Fertilisation and Implantation
After fertilisation, the fertilised egg — now called a zygote — travels along the fallopian tube towards the uterus, dividing rapidly as it goes. By the end of week three it has become a blastocyst and implanted into the lining of the uterus. Implantation can occasionally cause light spotting, known as implantation bleeding, which is sometimes mistaken for a light period.
Week 4 — The Embryo Begins
The blastocyst is now fully embedded in the uterine lining and has divided into two distinct parts — the part that will become your baby, and the part that will become the placenta. Human chorionic gonadotropin (hCG) — the hormone detected by a pregnancy test — is now being produced. This is usually when a home pregnancy test will give a positive result.
Weeks 5 and 6 — The Heart Begins to Beat
By week 5, your baby — now called an embryo — is about the size of a sesame seed, but development is happening at an extraordinary pace. The neural tube, which will become the brain and spinal cord, is forming. By week 6, the heart is beating. On an early scan, this heartbeat appears as a tiny flickering — one of the most moving things many parents will ever see.
The embryo is developing at a remarkable rate, with the foundations of all the major organ systems being laid down in these early weeks.
Weeks 7 and 8 — Facial Features Emerge
By week 7 your baby is around 1cm long. Tiny arm and leg buds are visible, and the face is beginning to take shape — dark spots where the eyes will be, a tiny opening where the mouth will form. The brain is developing rapidly and the heart is now beating around 150 times per minute — twice the rate of an adult.
By week 8 fingers and toes are beginning to form, still webbed but distinct. All of the major internal organs — heart, kidneys, liver, lungs — are present in early form and beginning to develop their function.
Weeks 9 and 10 — Moving for the First Time
Your baby — now referred to as a fetus rather than an embryo from around week 10 — is beginning to make spontaneous movements. You won't feel these yet, as the baby is far too small and the movements too gentle. But on an early scan at this stage, you may be able to see your baby wriggling.
Fingernails are forming. The face looks increasingly human. The tail that was present in the very early embryo has disappeared.
Weeks 11 and 12 — Fully Formed in Miniature
By week 12, your baby is around 6cm long and weighs approximately 14 grams — about the size of a lime. All the major structures are present. The genitals are forming, though it's usually too early to tell the sex on a scan at this stage. The baby can open and close its fists, and the kidneys are beginning to produce urine.
The risk of miscarriage drops significantly after week 12, which is why this is often referred to as the end of the "unsafe" period — though it's worth noting that the risk doesn't disappear entirely, just reduces substantially.
First Trimester Symptoms — What's Normal
The first trimester is infamous for being physically challenging, and for good reason. The hormonal changes happening in your body in these early weeks are dramatic, and they have wide-ranging effects.
Nausea and Morning Sickness
Nausea — with or without vomiting — affects the majority of pregnant women in the first trimester. Despite being called "morning sickness," it can strike at any time of day or night, and for many people it's present throughout the day.
It typically begins around week 5 or 6 and peaks around weeks 8 to 10, usually easing significantly by week 12 to 14. For some people it resolves completely by the second trimester. For others it lingers.
There are a few simple things that may help ease pregnancy sickness. Eating small, frequent meals can make a difference, as an empty stomach often makes nausea feel worse. Some people find it helpful to keep plain crackers or dry biscuits by the bed and eat one or two before getting up in the morning. Avoiding strong smells or foods that trigger nausea can also help, alongside staying hydrated by sipping cold water, ginger tea or flat lemonade throughout the day. Ginger, whether as biscuits, tea or sweets, has some reasonable evidence behind it for helping to reduce nausea. Acupressure wristbands, like the ones often used for travel sickness, may also work for some people. Rest is important too, as tiredness can make nausea feel much worse.
When to seek help: If you're unable to keep any food or fluid down, are losing weight, or are feeling dizzy and weak, speak to your GP or midwife. A condition called hyperemesis gravidarum (HG) — severe, persistent vomiting in pregnancy — affects around 1 in 100 pregnant women and requires medical treatment. It is not simply "bad morning sickness" — it is a serious condition that can lead to dehydration and malnutrition if not treated. If you are struggling to keep fluids down, please don't wait it out — seek help.
Extreme Tiredness
The exhaustion of the first trimester is frequently underestimated by those who haven't experienced it. It is not ordinary tiredness. It is a bone-deep fatigue that can make getting through a normal working day feel like running a marathon.
This is largely driven by the enormous increase in progesterone, which has a sedative effect, combined with the extraordinary amount of energy your body is putting into building a placenta and supporting your baby's rapid early development. Your blood volume is also increasing — by around 50% over the course of pregnancy — which places additional demands on the heart and circulatory system.
Rest as much as you can. Go to bed earlier. Take naps if possible. Don't push through exhaustion if you can avoid it — your body is doing something extraordinary and it needs the energy.
The good news: for most people, the extreme fatigue of the first trimester lifts significantly in the second trimester, as the placenta takes over hormone production and your body adjusts.
Breast Tenderness
Breasts often become extremely tender, heavy, and sensitive in early pregnancy — sometimes before a positive test. The areolas (the darker skin around the nipple) may also become larger and darker. These changes are driven by rising oestrogen and progesterone, preparing the breasts for feeding.
A well-fitting, supportive bra — possibly a soft crop-top style for sleeping — can help significantly.
Frequent Urination
The need to wee more frequently is common from very early in pregnancy, often before a missed period. It's caused by the increase in blood flow to the kidneys (which are working harder) and later in the first trimester by the growing uterus beginning to put pressure on the bladder.
Heightened Sense of Smell
Many pregnant women experience a dramatically heightened sense of smell in the first trimester, which is thought to be linked to the surge in oestrogen. This can be a significant contributor to nausea — certain smells that were previously neutral can become intensely triggering. Common culprits include cooking smells, coffee, perfume, petrol, and meat.
Bloating and Constipation
Progesterone relaxes smooth muscle throughout the body — including the muscles of the digestive tract. This slows digestion, which can cause bloating, gas, and constipation. Eating plenty of fibre-rich foods, drinking plenty of water, and staying gently active all help. If constipation is severe, speak to your GP or pharmacist about pregnancy-safe laxatives.
Food Aversions and Cravings
Changes in taste and smell can trigger strong food aversions in the first trimester — foods you previously enjoyed can become intolerable. Common aversions include meat, eggs, coffee, and strong-flavoured vegetables. Cravings — often for carbohydrate-rich or salty foods — are also very common.
Eat what you can manage. Bland carbohydrates are a staple of the first trimester for many people and that's completely fine. Focus on staying hydrated and getting some nutrition in rather than eating a perfectly balanced diet at this stage.
Mood Changes
The hormonal upheaval of early pregnancy can cause significant emotional volatility — mood swings, tearfulness, irritability, and anxiety are all common. This is not weakness or overreaction — it is a physiological response to the dramatic changes in your hormone levels.
If feelings of low mood, anxiety, or hopelessness are persistent or severe, speak to your GP or midwife. Antenatal depression is as real and as valid as postnatal depression, and you deserve support. You don't have to manage it alone.
Spotting and Implantation Bleeding
Light spotting in early pregnancy is relatively common and is not always a sign that something is wrong. Implantation bleeding (around the time the embryo implants in the uterine wall), cervical sensitivity, or a subchorionic haemorrhage (a small bleed near the placenta) can all cause light spotting that resolves without causing harm to the pregnancy.
However, any bleeding in pregnancy should always be assessed. Contact your GP, midwife, or early pregnancy unit (EPU) if you experience vaginal bleeding, so that the cause can be identified and you can be reassured or appropriately supported.
Warning Signs in the First Trimester
Seek prompt medical attention if you experience:
Heavy bleeding — more than light spotting, particularly if accompanied by cramping. This requires urgent assessment to rule out miscarriage or ectopic pregnancy.
One-sided pain — severe pain on one side of the abdomen, particularly if accompanied by bleeding, dizziness, or shoulder tip pain, can indicate an ectopic pregnancy — a pregnancy that has implanted in the fallopian tube rather than the uterus. Ectopic pregnancy is a medical emergency. Call 999 or go to A&E immediately.
Inability to keep fluids down — as described above, this requires medical attention.
Fever — a high temperature in pregnancy always warrants medical assessment.
What to Do in the First Trimester — Your Checklist
Book Your Booking Appointment
Your first step is to contact your GP, who will refer you to a midwife. Your booking appointment — usually around 8 to 10 weeks of pregnancy — is your first formal antenatal appointment. It's a long appointment where your midwife takes a detailed medical and family history, arranges your first blood tests, and discusses your options for antenatal care and place of birth.
Book as early as possible — midwife capacity varies by area and early booking ensures you're in the system.
Start Taking Folic Acid
If you haven't already, start taking folic acid immediately. The recommended dose is 400 micrograms (0.4mg) per day, taken from before conception until the end of the first trimester (12 weeks). Folic acid significantly reduces the risk of neural tube defects such as spina bifida.
If you have certain health conditions or are taking certain medications, your GP may recommend a higher dose (5mg) — check with your GP if you're unsure.
Most pregnancy multivitamins contain folic acid, but check the label to ensure the dose is correct.
Vitamin D
The NHS recommends that all pregnant women take 10 micrograms of vitamin D daily throughout pregnancy and breastfeeding. Most pregnancy vitamins contain this, but check.
Book Your Dating Scan
Your dating scan — also called the 12-week scan — is offered between weeks 10 and 14. It's usually arranged by your midwife at your booking appointment, but if you're very early in pregnancy, you can ask your GP about timing. This scan confirms your due date, checks for a heartbeat, and screens for chromosomal conditions as part of the combined screening test.
Review Your Medications
If you take any regular medications, speak to your GP as soon as possible. Some medications are not safe in pregnancy and may need to be changed or stopped. Never stop a prescribed medication without medical advice — discuss it with your GP first.
Review Your Lifestyle
Alcohol: The NHS advises that there is no known safe level of alcohol in pregnancy, and recommends avoiding alcohol entirely, particularly in the first trimester when the baby's organs are forming.
Smoking: If you smoke, stopping is one of the most important things you can do for your baby's health. Your midwife can refer you to specialist stop smoking support. Don't feel judged — reaching out for help takes courage and your midwife is there to support you.
Caffeine: The NHS recommends limiting caffeine to no more than 200mg per day during pregnancy — roughly equivalent to one mug of filter coffee. Tea, cola, energy drinks, and chocolate also contain caffeine and count towards this total.
Foods to avoid: Certain foods carry a risk of food poisoning or contain substances that can harm the developing baby. These include unpasteurised cheeses, pâté, raw or undercooked meat, raw shellfish, shark, swordfish, and marlin, and more than two portions of oily fish per week. The NHS website has a full, up-to-date list.
Exercise: Unless you have a specific medical reason not to, gentle exercise is safe and beneficial throughout pregnancy. If you were active before pregnancy, you can generally continue what you were doing with modifications as your pregnancy progresses. Avoid contact sports and anything with a risk of falling or abdominal impact.
Think About When to Tell People
There's no right or wrong answer to this. Many people wait until after the 12-week scan, when the risk of miscarriage has reduced and they have the reassurance of seeing their baby. Others tell close family or friends earlier for support, particularly if they're struggling with symptoms.
You might also want to think about telling your employer, particularly if your job involves physical demands, exposure to hazardous substances, or significant stress — you have a right to a risk assessment and adjustments once you've informed your employer of your pregnancy.
Register with a GP and Dentist
Make sure you and your baby are registered with a GP near your home. NHS dental treatment is free throughout pregnancy and for a year after the birth — register with a dentist if you're not already, and let them know you're pregnant at your next appointment.
Take Care of Yourself
This might sound obvious, but the first trimester is hard. The symptoms are real, the exhaustion is genuine, and the anxiety — particularly before the 12-week scan — can be significant. Be kind to yourself. Rest when you can. Eat what you can manage. Lean on the people you trust.
You are doing something extraordinary, even when it doesn't feel like it.
Frequently Asked Questions About the First Trimester
Is it safe to exercise in the first trimester? Yes, for most people. Gentle to moderate exercise is safe and beneficial. Walking, swimming, yoga, and cycling (on a stationary bike) are all good options. Avoid high-impact activity if you're experiencing significant nausea or bleeding, and always check with your midwife or GP if you're unsure.
Can I travel in the first trimester? Generally yes, though you may not feel up to it if you're experiencing significant nausea or fatigue. If you're travelling by air, be aware that some airlines restrict travel in late pregnancy — this is unlikely to apply in the first trimester, but check the airline's policy. Always take your maternity notes with you if you travel abroad in the second or third trimester.
When will I start showing? For most first-time parents, the bump doesn't become visible until the second trimester — typically around 12 to 16 weeks. If you've been pregnant before, you may show earlier. Body shape and size affect this significantly.
Is sex safe in the first trimester? Yes, unless your midwife or doctor has specifically advised otherwise. Sex does not cause miscarriage. You may find your desire changes significantly due to nausea, fatigue, and breast tenderness — this is completely normal.
Can I dye my hair in the first trimester? Most hair dyes are considered safe in pregnancy, particularly from the second trimester onwards. The evidence on first trimester hair dye is limited but not alarming. Many women choose to wait until after week 12 as a precaution, or use ammonia-free products. Discuss with your midwife if you're concerned.
From Little Village Antenatal
While it might feel early to be thinking about antenatal courses in the first trimester, this is actually a great time to start researching your options — particularly if you're due in a busy period of the year. Courses fill up quickly, and most recommend completing them by around 36 weeks.
At Little Village Antenatal, we offer comprehensive antenatal courses covering birth preparation, infant feeding, infant first aid, and the postnatal period, running from our base in Erith and serving families across Bexley, Dartford, Sidcup, Belvedere, and the wider Southeast London and Kent area.
We're FEDANT registered (National Register Entry Number: 13969). Find out more and view our upcoming courses here.
You've just embarked on the most extraordinary journey. We'd love to be part of it.
This blog is for informational purposes only and is not a substitute for advice from your midwife, GP, or healthcare team. If you have any concerns about your health or your baby's wellbeing during pregnancy, always seek medical advice promptly. In an emergency, call 999.