Blood pressure in the third trimester: understanding your readings
Learn what a normal reading means and when to contact your care team during the final trimester of pregnancy.
Important safety note: this article provides general information only and does not replace personalised medical advice. If you are in the third trimester and your readings are consistently at or above 140/90, or you have headaches, visual disturbances (spots or flashing lights), sudden swelling of your face, hands or feet, or pain under your ribs, contact your midwife or maternity unit immediately. Do not wait for your next scheduled appointment. In an emergency, call 999.
One clinic reading captures your blood pressure at one moment, but may miss how it changes over time. The third trimester is when monitoring becomes especially important. Your body is working hard, blood volume is significantly higher than before pregnancy, and the risk of conditions such as pre-eclampsia, which usually emerges after 20 weeks, is highest. Knowing what readings mean, and when to call rather than simply log one, is useful in these final weeks.
This article explains blood pressure in late pregnancy, including what the numbers mean, why context matters as much as one reading, and when to seek care. Your midwife or GP should interpret your individual readings. This background can help you have more informed conversations with them.
What your blood pressure readings mean
A blood pressure reading contains two numbers. The higher, systolic number, measures arterial pressure when your heart beats. The lower, diastolic number, measures pressure while your heart rests between beats. Both are measured in millimetres of mercury (mmHg).
In pregnancy, a normal reading is generally around 120/80 or below, although your personal baseline may differ. Blood pressure usually falls slightly during the first half of pregnancy as blood vessels relax to accommodate increased blood flow. During the second half, especially the third trimester, it generally returns towards pre-pregnancy levels or rises slightly above them.
Clinical guidelines generally describe readings of 140/90 and above as elevated in pregnancy. A reading at or above this level on two occasions, at least four hours apart, usually needs clinical assessment. If you are unsure which ranges apply to your care plan, ask your midwife. Your history and risk factors affect what your care team monitors and when they want to hear from you.
Why one reading may tell you less than expected
Blood pressure varies during the day and with many factors, including activity, stress, posture, caffeine, and how long you have been sitting or standing. A reading after rushing to a clinic appointment may not represent your resting baseline.
This is why home monitoring can be useful in pregnancy, and why a consistent log matters more than one number. If you take readings at home, your midwife will generally advise sitting quietly after resting for a few minutes, using the same arm each time and taking readings at roughly the same time of day. Readings taken under consistent conditions provide more information than one clinic reading after climbing three flights of stairs.
The main value of a week's home readings is showing your trend. A slightly high reading one morning followed by a normal one differs from pressure that has risen steadily over two weeks. Your midwife can assess a trend, but not a single snapshot.
What "white coat hypertension" means and why it matters
White coat hypertension means consistently higher readings in clinical settings but normal readings at home. It is well documented in the general population and also occurs in pregnancy. If your appointment readings are consistently higher than those at home, tell your midwife. She may ask you to keep a home monitoring log to establish your true baseline.
However, do not use it as reassurance when your home readings are also high. If both home and clinic readings are elevated, the pattern needs assessment, whether or not anxiety contributes. White coat hypertension matters when it explains the difference, not when it dismisses the concern.
Symptoms that change the picture
A reading above 140/90 is important on its own. But certain symptoms, alongside elevated blood pressure or independently during the third trimester, need prompt clinical attention whatever a home monitor shows.
These include a severe or persistent headache that does not respond to paracetamol; visual disturbances such as spots, flashing lights, or blurred vision; upper abdominal pain or tenderness, particularly on the right below the ribs; sudden or severe swelling of the face, hands, or feet; and feeling generally unwell in a way that is hard to attribute to normal third-trimester discomfort.
If you have any of these symptoms, especially together, contact your midwife or maternity unit straight away, or call 111 if you cannot reach them. Do not record them and wait for your next appointment. These symptoms should be reported, not monitored.
How consistent logs support your care
If you have a home blood pressure monitor, keeping a consistent daily record has real clinical value, especially in the final trimester. It need not be elaborate. Record the date, time, and two numbers. Over several weeks, this creates a timeline showing your midwife whether your pressure is stable, rising, or varying unpredictably.
That timeline gives context at your next appointment. Rather than seeing one reading in isolation, your midwife can interpret it alongside the record. A reading of 128/84 after two weeks of consistent 120/78 readings differs from 128/84 at the peak of a rising trend. The number is identical, but the story is different.
Daily monitoring is not a replacement for clinical assessment. It makes each clinical contact more informative. Your midwife makes the decisions, while a consistent record gives her more information to use.
What monitoring cannot do
Home blood pressure monitoring cannot diagnose pre-eclampsia or any other condition. Diagnosis requires clinical assessment, including a urine test for protein and a full clinical evaluation. If your readings cause concern, call your midwife rather than trying to interpret them yourself.
High readings can also result from issues unrelated to pregnancy complications, including the wrong cuff size, poor posture, movement before measuring, or a monitor needing recalibration. If a reading seems unexpectedly high, take two or three more at the same time, a few minutes apart, and check your technique is consistent before responding to the first number.
In the third trimester, paying attention to how you feel and keeping a consistent record of what you notice can be genuinely valuable. Trusting your instincts and contacting your midwife when something feels wrong is equally important. These are not competing approaches: the log supports the conversation, not the other way round.
This article is for information only and does not replace professional medical advice. Discuss blood pressure ranges and thresholds with your midwife or GP in the context of your individual care plan. If you are concerned about your blood pressure or have any symptoms described here, contact your midwife, maternity unit, or call 111. In an emergency, call 999.