At 7 weeks the embryo is about 9 mm — blueberry-sized, and more than double what it was a week ago. Growth this fast is why the first trimester is so demanding on you even though nothing is visible from the outside.
The short answer: the brain is growing faster than any other organ, the arms are lengthening, nostrils have appeared and the kidneys are in position. For you, rising blood volume brings breathlessness and light-headedness, the mucus plug forms in the cervix as an infection barrier, and progesterone makes gums swell and bleed. Dental care is safe and worth booking.
Your baby this week
Brain development dominates this week. Neurons are being generated at a rate that will not be matched again, and the brain is folding into the structures that become the cerebral hemispheres. The head is disproportionately large compared with the body, and will stay that way for months.
The arm buds have lengthened and now have a distinct paddle at the end where the hand will form; the leg buds are a little behind. Nostrils are visible on the face, the eyes are developing lenses and retinas beneath a covering of skin, and the mouth and tongue are taking shape.
The kidneys are in position and preparing to start their first job — producing urine, which will make up a large share of the amniotic fluid later on. The embryo has started making small spontaneous movements. At 9 mm and with no strength behind them, they are far too slight to feel; first movements are typically felt between 16 and 24 weeks.
Your body this week
Your circulating blood volume has begun rising and will keep climbing for months, eventually reaching roughly 40–50% above your pre-pregnancy level by the middle to later part of pregnancy. That expansion, combined with progesterone relaxing blood vessel walls, is why blood pressure often falls in the first half of pregnancy and why standing up quickly can make you light-headed.
Progesterone also increases your respiratory rate, so a mild sense of breathlessness — particularly on stairs — is common and normal this early, long before the uterus is pressing on anything.
In the cervix, a thick mucus plug forms and seals the canal. It is a genuine physical barrier against infection ascending from the vagina, and it remains until close to labour.
Skin often becomes more reactive now. Increased melanocyte-stimulating hormone makes you more prone to burning and to pigmentation, so daily sunscreen is worth starting — it is the same mechanism behind the pigmentation changes that appear later.
Tests and appointments
Nothing routine falls at 7 weeks, but your booking appointment should already be arranged for somewhere between 8 and 12 weeks. This is also a sensible week to book a dental check-up. Dental treatment is safe in pregnancy, gum problems are more common now, and in many places routine dental care during pregnancy is free.
✅ Worth doing this week
- Drink 1.5–2 litres of water a day — the expanding blood volume and your kidneys both need it
- Stand up slowly, especially from a bath or bed, while your blood pressure is low
- Switch to a soft toothbrush and an alcohol-free mouthwash; keep flossing rather than stopping because of bleeding
- Book a dental appointment and tell them you are pregnant
- Wash your hands after being out — immune tolerance of the pregnancy means infections can hit harder
When to call your doctor
Call the same day if: you have bleeding heavier than spotting, severe or one-sided abdominal pain, shoulder-tip pain, fainting, breathlessness at rest or with chest pain or palpitations, a temperature above 38°C, or burning on passing urine. Ectopic pregnancy most commonly presents between weeks 5 and 10, so one-sided pain in this window always needs assessing rather than watching.
FAQ — 7 weeks pregnant
How big is the baby at 7 weeks?
About 9 mm crown to rump — roughly a blueberry, and more than double last week. The embryo has grown longer arms, visible nostrils, and is beginning to make small movements, though you will not feel anything for several months yet.
Why am I dizzy and short of breath at 7 weeks?
Progesterone relaxes the walls of your blood vessels, which lowers blood pressure, and it also increases your breathing rate — so mild breathlessness and light-headedness when you stand up quickly are both common in the first trimester. Stand up slowly, keep fluids up, and eat regularly. Dizziness with chest pain, palpitations, fainting, or breathlessness at rest is different and needs same-day assessment.
What is the mucus plug?
A thick collection of cervical mucus that forms in the cervical canal during early pregnancy and seals it, acting as a barrier against infection travelling up from the vagina. It stays in place for most of the pregnancy and is released near labour — the "show". You will not notice it forming now.
Why are my gums bleeding?
Progesterone increases blood flow to the gums and exaggerates the inflammatory response to plaque, so gums swell and bleed more easily — commonly called pregnancy gingivitis, and it affects a large share of pregnant women. Use a soft brush, keep flossing gently, and see a dentist: dental care is safe in pregnancy and untreated gum disease has been linked to preterm birth. Tell the dentist you are pregnant so X-rays are shielded or deferred.
Week 7 at a glance
At 7 weeks the embryo is roughly 9 mm — blueberry-sized and more than double last week — with the brain growing faster than any other organ, nostrils visible, arms lengthening and kidneys in position. The first small spontaneous movements begin, far too slight to feel. For you, blood volume is rising and progesterone is relaxing your vessels and raising your breathing rate, which together explain the light-headedness and mild breathlessness. The mucus plug forms in the cervix as an infection barrier, and gums become swollen and prone to bleeding — a good week to book a dentist, since treatment is safe and untreated gum disease matters.
Inside Baby Novum: the health section logs blood pressure alongside symptoms, so a pattern of light-headedness can be seen against real readings rather than recalled. Appointment reminders cover the booking visit and the dental check most people forget.