Glossary: Terms Starting with "F"

The fertile window is the span of days in your menstrual cycle when having unprotected sex can result in pregnancy. It includes the five days before ovulation and the day of ovulation itself, because sperm can survive in the reproductive tract for up to five days. For a typical 28-day cycle this window falls roughly between days 10 and 15, but the exact timing shifts with cycle length. Tracking cervical mucus changes, basal body temperature, or using an ovulation predictor kit can help you identify your personal fertile window more accurately than calendar counting alone.

Related: Ovulation, cervical mucus, BBT

Fetal age, also called conceptional age or embryonic age, counts how long an embryo or fetus has actually existed since the moment of fertilisation. Because ovulation and conception typically occur about two weeks after the start of your last menstrual period, fetal age is usually roughly two weeks less than gestational age. For example, at 12 weeks gestational age, the fetus is approximately 10 weeks old by fetal age. This distinction matters most in reproductive medicine and embryology research, but in everyday antenatal care your doctor will use gestational age for all scheduling and monitoring decisions.

Related: Gestational age, conception

The first trimester covers weeks 1 through 13 of pregnancy, and it is one of the most critical periods for your baby's development. During these weeks, the fertilised egg implants in the uterus, and all major organs and body systems begin to form, including the heart, brain, spinal cord, and limbs. Many women experience morning sickness, fatigue, and breast tenderness during this time. Your first prenatal appointment will usually happen around week 8 to 10, where your doctor will confirm the pregnancy, check for a heartbeat, and order blood tests. Avoiding alcohol, raw foods, and certain medications is especially important during this window.

Related: Embryo, morning sickness

From week 9 of pregnancy until birth, your developing baby is medically called a fetus. By this stage, all the major organs have begun to form and will spend the rest of the pregnancy maturing and growing. The fetus develops the ability to swallow, kick, hear sounds, and respond to light as pregnancy progresses. Regular ultrasound scans during the second and third trimesters monitor fetal growth, position, and wellbeing. If scans show that growth is slower than expected, your doctor may refer to intrauterine growth restriction (IUGR) and arrange more frequent monitoring. In everyday conversation, most parents and midwives simply say baby.

Related: Embryo, fetal development

Fetal cardiac activity refers to the flickering movement of the developing heart detected by ultrasound. On a transvaginal scan, this can sometimes be seen as early as 6 weeks of pregnancy, though 6.5 to 7 weeks is more reliable. At this stage it is detected visually on ultrasound rather than heard. From around 10 to 12 weeks onward, a handheld Doppler device can pick up the heartbeat audibly at prenatal appointments. A normal fetal heart rate in early pregnancy ranges from about 90 to 180 beats per minute, and it tends to increase through the first trimester before settling into a steadier range.

Related: Doppler, ultrasound

Fetal movement includes all the ways your baby moves inside the womb, from early flutters and rolls to strong kicks and jabs in the third trimester. Most mothers notice consistent movement from around 24 to 28 weeks onward. Paying attention to your baby's normal pattern of movement is one of the most important things you can do in the second half of pregnancy. Every baby has its own rhythm of active and quiet periods. A noticeable change in your baby's usual movement pattern, especially a significant decrease, is a reason to contact your care provider the same day rather than waiting for your next appointment.

Related: Quickening, kick counts

Full term is the birth timing category covering 39 weeks 0 days through 40 weeks 6 days of pregnancy. This is now considered the optimal window for delivery in uncomplicated pregnancies. By 39 weeks, a baby's lungs, brain, liver, and immune system are well developed and ready for life outside the womb. Babies born at full term are less likely to need NICU care, tend to feed more easily, and generally have better long-term health outcomes than those born even one or two weeks earlier. If your pregnancy is low-risk and progressing normally, your care team will aim to let labour begin naturally within this window.

Related: Early term, late term

Folic acid is the synthetic form of folate, a B vitamin that plays a critical role in forming your baby's brain and spinal cord. Getting enough folic acid in the weeks before conception and through the first 12 weeks of pregnancy significantly reduces the risk of neural tube defects such as spina bifida and anencephaly. The recommended dose for most women is 400 micrograms daily, though women with a history of neural tube defects or certain medical conditions may need a higher dose of 5 mg. It is found in leafy greens, legumes, and fortified foods, but a supplement is the most reliable way to meet the target.

Related: Neural tube, prenatal vitamin

Femur length (FL) is the ultrasound measurement of your baby's thigh bone, the longest bone in the body. It is recorded from around 14 weeks onward and is one of four standard biometric measurements used to estimate fetal age and weight. FL helps confirm whether your baby's skeletal development is progressing normally for gestational age. Very short femur length relative to other measurements can sometimes prompt further assessment, though a wide range of normal values exists across different ethnicities. Your obstetrician will always interpret FL alongside other measurements rather than in isolation.

Related: EFW, anatomy scan

Fundal height is the distance in centimetres measured from the top of your pubic bone to the top of your uterus (the fundus). Your midwife or obstetrician measures it with a tape measure at antenatal visits from around 20 weeks onward. As a rough guide, the fundal height in centimetres usually matches your gestational week, give or take two centimetres. It is a quick, inexpensive way to track whether your uterus is growing as expected. If the measurement is consistently small or large for your dates, your doctor will likely order an ultrasound to investigate further.

Related: Growth scan, uterus

A fetal Doppler is a handheld device that uses ultrasound waves to detect and amplify your baby's heartbeat. In clinical settings, midwives and obstetricians use Dopplers at antenatal check-ups to confirm the heartbeat and check its rate. Some parents purchase home Dopplers to listen between appointments. However, home use carries risks: it is easy to mistake your own pulse or placental sounds for your baby's heartbeat, and finding a heartbeat at home can give false reassurance if something is actually wrong. If you are worried about your baby's movements, contact your hospital rather than relying on a home Doppler.

Related: Fetal heartbeat, prenatal visit

False labour refers to contractions or other labour-like sensations that feel convincing but do not cause the progressive cervical changes needed for birth. Contractions may be uncomfortable, come somewhat regularly for a while, and then slow down or stop on their own. Unlike true labour, they tend to ease with a warm bath, rest, or a change of activity. False labour is very common in the weeks before your due date and does not mean anything is wrong. It can be frustrating, especially for first-time parents, but it is your body gradually preparing for the real event.

Related: Braxton Hicks, prodromal labor

The first stage of labor begins with your first regular contractions and ends when your cervix is fully dilated to 10 centimeters. It is divided into two phases: the latent phase, where the cervix dilates from 0 to 6 centimeters, and the active phase, where dilation speeds up from 6 to 10 centimeters. Contractions grow longer, stronger, and closer together as this stage progresses. For first-time mothers, this stage can last 12 to 20 hours or more. Staying mobile, using breathing techniques, and keeping well-hydrated can help you cope with the intensity.

Related: Latent phase, active labor

Fetal monitoring tracks your baby's heart rate during labor to make sure the baby is coping well with contractions. A healthy baby shows a heart rate that rises and falls in response to movement and contractions. Two main methods are used: intermittent auscultation, where a midwife listens with a handheld Doppler every 15 to 30 minutes, and continuous electronic monitoring using a CTG machine strapped to your belly. Continuous monitoring is recommended if your labor is high-risk, such as after an induction, if you have an epidural, or if concerns arise during labor.

Related: CTG, Doppler

Forceps are smooth, curved metal instruments that look like large salad tongs. During a forceps delivery, a skilled doctor gently places them around the sides of the baby's head and applies careful traction during contractions to help ease the baby out. Forceps may be used when the second stage of labor is prolonged, when the mother has a medical condition that limits pushing, or when the baby needs to be born quickly due to a drop in heart rate. An episiotomy is often performed at the same time to create more space. Forceps delivery requires significant training and experience.

Related: Assisted birth, vacuum

Formula feeding means giving your baby commercial infant formula instead of, or in addition to, breast milk. Infant formula is designed to closely mimic the nutritional profile of breast milk, providing the protein, fat, carbohydrates, vitamins, and minerals babies need to grow. Parents choose formula for many reasons, including low milk supply, medical conditions, returning to work, or personal preference. All choices are valid. To formula feed safely, always use boiled and cooled water, measure scoops precisely, and never water down formula to make it stretch further. Bottles and teats should be sterilised after every feed, especially in the first six months.

Related: Bottle feeding, combo feeding

Fetal growth restriction (FGR) means a baby is not growing as fast as expected in the womb, resulting in an estimated weight below the 10th percentile for gestational age. It can happen because the placenta is not delivering enough oxygen and nutrients, or due to maternal conditions like high blood pressure, preeclampsia, or infections. FGR raises the risk of stillbirth, premature birth, and long-term health challenges for the baby. Doctors use regular ultrasound scans and Doppler blood flow studies to track the baby's growth and placental function, and may recommend early delivery if the baby shows signs of distress.

Related: IUGR, EFW

The fourth trimester is the informal name for the first three months after birth, a time of enormous transition for both baby and parents. Newborns arrive neurologically immature and spend these weeks adjusting to life outside the womb. They crave constant closeness, warmth, and feeding, which is completely normal. For parents, this period brings sleep deprivation, identity shifts, and the steep learning curve of caring for a newborn. Understanding that unsettled behavior in a newborn is developmentally expected, not a sign of bad parenting, can help reduce anxiety and build confidence during what is often the most overwhelming stretch of early parenthood.

Related: Postpartum, newborn care