Glossary: Terms Starting with "B"

Basal body temperature (BBT) is your lowest resting body temperature, measured first thing in the morning before you get up, talk, or eat. After ovulation, the hormone progesterone causes BBT to rise by about 0.2 to 0.5 degrees Celsius and stay elevated until your next period. By charting these daily readings over several cycles, you can identify a pattern that reveals when you ovulate. This helps you time intercourse in future cycles, since the rise confirms ovulation has already occurred. A consistent BBT chart can also be shared with your gynaecologist if you are investigating fertility concerns.

Related: Ovulation, luteal phase

Beta hCG (human chorionic gonadotropin) is a hormone produced by the placenta after a fertilised egg implants in the uterus. A blood test measures the exact level in mIU/mL, giving more precise information than a urine pregnancy test. In early pregnancy, doctors track two readings taken 48 hours apart. A healthy pregnancy typically sees levels double every two days. Very low or slowly rising numbers can signal a possible miscarriage or ectopic pregnancy, while unusually high levels may indicate twins or a molar pregnancy. Your doctor uses trends over time, not a single reading, to assess how your pregnancy is progressing.

Related: hCG, doubling time

A birth partner is the person you choose to be by your side during labor and birth, offering continuous support and advocacy throughout the process. This can be your spouse, a parent, a close friend, or a hired doula. A good birth partner helps you stay calm between contractions, communicates your preferences to the medical team, fetches water, and simply holds your hand when words are not enough. Being well-prepared together matters: attending antenatal classes as a pair, discussing your birth preferences in advance, and agreeing on when to head to the hospital are all steps that make a real difference.

Related: Doula, support person

A birth plan is a written summary or conversation that outlines your preferences for labor, delivery, and immediate newborn care. It may cover pain relief options, preferred delivery positions, who cuts the cord, delayed cord clamping, skin-to-skin contact, and feeding intentions. While no one can guarantee that birth will follow a script, sharing your preferences helps the care team understand what matters most to you, and opens up an important conversation about what is realistically possible. Keep it concise, ideally one page, and frame preferences as wishes rather than demands so the team can work with you flexibly as the situation evolves.

Related: Pain relief, skin-to-skin

Biparietal diameter (BPD) is an ultrasound measurement taken across the widest part of your baby's skull, from one side of the head to the other. It is one of the key measurements used to estimate gestational age in early pregnancy and to monitor fetal growth as pregnancy progresses. BPD is measured in millimetres and plotted against standard growth charts. A result that falls outside the normal range does not automatically indicate a problem, as head shape, fetal position, and ethnic variation all affect the reading. Your obstetrician will always interpret BPD alongside other measurements before drawing any conclusions.

Related: HC, EFW

Blood pressure is measured at every antenatal visit because it is one of the earliest warning signs of complications such as gestational hypertension and pre-eclampsia. A normal reading is usually below 130/85 mmHg in pregnancy. Readings consistently at or above 140/90 mmHg require further assessment, including urine tests for protein and blood tests. Pre-eclampsia can develop rapidly and is dangerous for both mother and baby if left untreated. Even if you feel fine, a high reading should never be ignored. Your care team will decide whether monitoring at home, medication, or admission is needed based on the full clinical picture.

Related: Preeclampsia, gestational hypertension

Braxton Hicks contractions are occasional, painless tightenings of the uterus that can start as early as the second trimester and become more noticeable in the third. They are the uterus practising for labour, but unlike true labour contractions, they are irregular, do not increase in frequency or intensity, and usually ease off when you change position, drink water, or rest. They feel like a squeezing or hardening across the abdomen that lasts 30 to 60 seconds. If contractions become regular, grow stronger, or come with back pain or fluid leakage, contact your doctor or head to the delivery suite.

Related: False labor, contractions

Bloody show is a small amount of blood-tinged or pink mucus discharge that appears as the cervix begins to dilate and efface in preparation for labour. It happens because tiny blood vessels in the cervix break as it stretches and softens. Bloody show can occur hours or even a few days before active labour begins, and it is considered a normal sign that your body is progressing. It often appears after a cervical examination by your doctor or midwife. The amount is usually small, roughly a teaspoon or less, and is mixed with mucus rather than appearing as fresh, flowing blood.

Related: Mucus plug, dilation

A birth pool is a large, inflatable or permanent tub filled with warm water that you can use during labor or for the actual birth. Warm water immersion helps ease contraction pain by relaxing your muscles and reducing pressure on your body. It can lower the need for pain medication and help you feel more in control. You can enter the pool in active labor and exit at any time. The water temperature is kept around 37 degrees Celsius to keep you comfortable and prevent your baby from overheating. A midwife monitors both of you throughout.

Related: Water birth, water immersion

Breech presentation means your baby is positioned with their bottom, feet, or knees pointing toward your cervix instead of their head. This occurs in about 3 to 4 percent of full-term pregnancies. Most babies turn head-down on their own before 36 weeks, so a breech position found at an earlier scan is not usually a cause for alarm. However, if your baby remains breech by 36 weeks, your obstetrician will discuss your options, which may include a procedure called external cephalic version to turn the baby, or planning a caesarean section for a safer delivery.

Related: Cephalic, ECV

Back labor refers to intense, persistent pain felt in the lower back during contractions, and sometimes between them. It is most common when the baby is in the occiput posterior (OP) position, meaning the baby's skull presses against your spine and tailbone. The sensation is often described as deep, aching pressure that does not fully ease between contractions. Comfort measures include counter-pressure applied firmly to the lower back by a partner or doula, warm compresses, changing positions such as hands-and-knees, or hydrotherapy if available. An epidural is also effective at relieving back labor pain.

Related: OP position, contractions

Bilirubin is a yellow pigment produced when the body breaks down old red blood cells. Newborns have a higher turnover of red blood cells than adults, and their livers are not yet fully efficient at processing and excreting bilirubin, so levels can rise quickly after birth. Bilirubin is measured via a blood test or a non-invasive skin device called a transcutaneous bilirubinometer. The result is plotted on a chart that takes into account the baby's age in hours, gestational age, and risk factors. Doctors use this to decide whether the baby needs phototherapy or simply more frequent feeding and monitoring.

Related: Jaundice, phototherapy

Baby blues are a very common emotional adjustment that affects up to 80 percent of new mothers in the first one to two weeks after birth. You may feel weepy, irritable, anxious, or emotionally fragile even when things are going well. These feelings are caused by the dramatic drop in oestrogen and progesterone that happens right after delivery, combined with sleep deprivation and the enormous life change of becoming a parent. Baby blues are temporary and usually resolve on their own by day 10 to 14. Rest, practical help from family, honest conversations, and gentle reassurance are the most useful supports during this brief window.

Related: PPD, hormones