What develops when: heartbeat, brain, pain, viability
Two clocks are in use: doctors count pregnancy weeks from the last menstrual period (LMP), about two weeks before fertilization; embryology counts from fertilization. The heart tube starts beating about 22 days after fertilization (about 5 weeks LMP) and is seen on ultrasound at about 6-7 weeks LMP; its four chambers form later (by about week 7 after fertilization). The neural tube closes by the end of week 4 after fertilization, and the cortex is built over roughly weeks 12-30 LMP. Whether and when a fetus can feel pain is disputed: the UK's RCOG (2022) says pain before 28 weeks is 'unlikely', while Derbyshire and Bockmann (2020) say it cannot be ruled out from about 12 weeks. Survival outside the womb is now reported from 21-22 weeks LMP with intensive care, and depends heavily on the hospital.
The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Lifepaper
During the third week, the FHF fuses at the midline to form the primitive heart tube, which starts to beat at around embryonic day 22 and eventually gives rise to the LV and parts of the right and left atria
Clock: days after fertilization ('embryonic day'). Day 22 after fertilization is about 5 weeks 1 day LMP. The same review says 'The initiation of the first heart beat via the primitive heart tube begins at gestational day 22, followed by active fetal blood circulation by the end of week 4' and 'Blood flow and contraction causes peristaltic pumping motion in the linear heart tube'. So peer-reviewed cardiology describes the early heart tube as beating and pumping blood, weeks before the four chambers exist. (FHF = first heart field; LV = left ventricle.)
Fetal development, weeks 6 to 7 (MedlinePlus)statement
Your baby's heart continues to grow and now beats at a regular rhythm. This can be seen by vaginal ultrasound. Blood pumps through the main vessels.
Clock: weeks from LMP (the page's stated convention). The NIH's consumer encyclopedia uses 'heart' and 'beats' for weeks 6-7. The same page lists, at week 10, 'Fetal heart tones may be detectable by Doppler testing', and at week 22, 'Your baby's heartbeat can be heard with a stethoscope.'
Embryology, Neural Tube (StatPearls)textbook
By the end of week three gestation after gastrulation, the notochord induces the lateral edges of the ectoderm to begin to form the neural folds. … By the end of week four, the formation of the neural tube will separate from the overlying ectoderm, and its structure will be complete.
Clock: weeks of development after fertilization (gastrulation is in the third week after fertilization), so the neural tube, which becomes the brain and spinal cord, is closed by about 6 weeks LMP. MedlinePlus (LMP clock) lists for weeks 6-7: 'Your baby's brain forms into 5 different areas. Some cranial nerves are visible.'
RCOG Fetal Awareness Evidence Review (section 2.1, spontaneous fetal motor behaviour)statement
Advances in ultrasound recording, including three-dimensional rendering, and dynamic magnetic resonance imaging (MRI) have provided new insights into the onset and maturation of fetal movements (Einspieler et al., 2021) from as early as 7.5 weeks of gestation. Evidence from animal models suggests that these early large scale muscle movements are spontaneously generated by neurons in the spinal cord and do not require a sensory stimulus to trigger them.
Clock: weeks of gestation (LMP-equivalent in this review). Movement is seen on ultrasound from about 7.5 weeks; the same section says 'Complex spontaneous movements of the hands towards the eyes, mouth and other regions have been observed from 18 weeks of gestation.' The mother usually feels movement later: MedlinePlus puts 'quickening' at weeks 19-21 LMP. Movement shows a living, developing nervous system; by itself it is not evidence of pain or awareness, as the RCOG notes.
Multi-Dimensional Human Embryo: Carnegie Stages 17-23textbook
Most embryos at stage 20 are approximately 50-51 postovulatory days old and measure 21-23 mm in length. Distinguishing criteria for this stage include upper limbs slightly bent at the elbows, short stubby fingers, hands curving over the cardiac region but still far apart from each other
Clock: days after ovulation (≈ fertilization), so add about 2 weeks for LMP. Stage 17 (~41 days): 'distinct digital rays in the hand plate'. Stage 20 (~50-51 days, ≈9 weeks LMP): 'short stubby fingers'. Stage 21 (~52 days): 'the toes are distinct'. Stage 23 (~56-57 days, end of the embryonic period, ≈10 weeks LMP): 'the external genitalia are well developed but not always sufficiently to distinguish the embryo's sex'. MedlinePlus (LMP) lists 'Genitals appear' and 'Nails appear on the fingers and toes' at weeks 11-14.
Reconsidering fetal painpaper
Overall, the evidence, and a balanced reading of that evidence, points towards an immediate and unreflective pain experience mediated by the developing function of the nervous system from as early as 12 weeks. That moment is not categorical, fetal development is continuous and not an event, and we recognise that some evidence points towards an immediate and unreflective pain not being possible until later.47 Nevertheless, we no longer view fetal pain (as a core, immediate, sensation) in a gestational window of 12–24 weeks as impossible based on the neuroscience.
The same researcher, 14 years on, now co-writing with a pro-life author ('We have divergent views regarding the morality of abortion, but have come together to address the evidence for fetal pain'). Their main argument: 'Even if the cortex is deemed necessary for pain experience, there is now good evidence that thalamic projections into the subplate, which emerge around 12 weeks’ gestation, are functional and equivalent to thalamocortical projections that emerge around 24 weeks’ gestation.' They recommend: 'Fetal analgesia and anaesthesia should thus be standard for abortions in the second trimester, especially after 18 weeks when there is good evidence for a functional connection from the periphery and into the brain.' Be precise about the limits: they say the evidence 'cannot definitively rule out fetal pain before 24 weeks' (not that it proves it), and 'We argue that abortions before 13 weeks’ gestation do not involve any meaningful likelihood of pain for the fetus.' The paper does not say '15 weeks'. Clock: 'weeks’ gestation', not further defined in the passages read.
Between-hospital variation in treatment and outcomes in extremely preterm infantspaper
Overall rates of active treatment ranged from 22.1% (IQR, 7.7 to 100) among infants born at 22 weeks of gestation to 99.8% (IQR, 100 to 100) among those born at 26 weeks of gestation. … Hospital rates of active treatment accounted for 78% and 75% of the between-hospital variation in survival and survival without severe impairment, respectively, among children born at 22 or 23 weeks of gestation
Births 2006-2011 at 24 US centres. Overall survival was 5.1% at 22 weeks and 81.4% at 26 weeks, but most 22-week babies were not given active treatment. The point for viability arguments: at 22-23 weeks, whether a baby survives depends heavily on whether the hospital tries. Clock: gestational age in completed weeks as used in obstetrics (LMP-based).
Mortality, In-Hospital Morbidity, Care Practices, and 2-Year Outcomes for Extremely Preterm Infants in the US, 2013-2018paper
Survival to discharge was 10.9% (60/549) for live-born infants at 22 weeks and 94.0% (2267/2412) at 28 weeks. Survival among actively treated infants was 30.0% (60/200) at 22 weeks and 55.8% (535/958) at 23 weeks.
10,877 infants born 2013-2018 at 19 US academic centres. Survivors often have serious problems: among those followed up, '21.2% (512/2419) had severe neurodevelopmental impairment' and '48.7% (1198/2458) had no or mild neurodevelopmental impairment'. These are academic centres, so survival elsewhere may be lower. Clock: 'weeks' gestational age' (obstetric, LMP-based).
Most premature baby (Guinness World Records): Nash Keen, 21 weeks 0 daysevent
The most premature baby is Nash Keen, who was born to Mollie and Randall Keen (all USA) at 9.51 a.m. on 5 July 2024 at University of Iowa Health Care in Iowa City, Iowa, USA, at a gestational age of exactly 21 weeks, or 147 days, making him 133 days premature. … Nash surpassed the previous record by one day: Curtis Zy-Keith Means (USA) was born to Michelle Butler on 5 July 2020 at the University of Alabama at Birmingham Hospital in Alabama, USA, at a gestational age of 21 weeks 1 day, or 148 days, making him 132 days premature.
Curtis Means (UAB, 2020) is no longer the record holder; Nash Keen took the title in 2025. Clock: LMP (147 days = 21 weeks; term counted as 280 days), i.e. about 19 weeks after fertilization. He weighed 285 g (10 oz). Iowa's hospital says it has 'begun to treat some 21-week babies if their parents wish us to', while also noting 21-week babies 'are considered too early to be offered intensive care in most hospitals'. Records are exceptional cases, not typical outcomes. UAB's own 2021 release confirms the Curtis Means details ('at a gestational age of 21 weeks 1 day or 148 days, making him 132 days premature'; twin sister C’Asya died a day after birth).
Fetal development (MedlinePlus Medical Encyclopedia)statement
Because it's impossible to know exactly when conception occurs, gestational age is measured from the first day of the mother's last menstrual cycle to the current date. It is measured in weeks. This means that during weeks 1 and 2 of pregnancy, a woman is not yet pregnant. … In your 40th week of pregnancy, it has been 38 weeks since conception
The key to every date on this page. Clinical 'weeks of pregnancy' (gestational age) count from the last menstrual period (LMP), about two weeks before fertilization. Embryology texts usually count from fertilization (or ovulation). So 'day 22 after fertilization' is about 5 weeks LMP, and '6 weeks pregnant' is an embryo about 4 weeks old. Each entry below says which clock it uses.
The Transitional Heart: From Early Embryonic and Fetal Development to Neonatal Lifepaper
The development of the heart begins as early as the third week of gestation with the 4-chamber fetal heart formed by gestational week 7.
Clock: this review counts 'gestation' from fertilization (it puts heart-tube fusion in 'the third week'), so week 7 here is roughly 9 weeks LMP. That fits ACOG's point that the chambers are not yet formed at the 6-weeks-LMP stage targeted by 'heartbeat' laws; it does not show there is no beating heart then (see the previous entry).
RCOG Fetal Awareness Evidence Review (section 3, cortex and thalamocortical development)statement
They reach their final location on the superficial surface of the brain from 12 weeks of gestation, with this process largely complete by approximately 30 weeks … mapping the fetal age for each of the key stages of fibre outgrowth from the thalamus (beginning at 8–9.5 weeks), path-finding (9–14 weeks), "waiting" in the cortical subplate region (14–22 weeks), (2 weeks earlier in somatosensory cortex than visual and other cortices) and ingrowth in the cortical plate (23–24 weeks)
Clock: 'weeks of gestation'; the review treats gestation as equivalent to postmenstrual age (LMP). The cortex is built over roughly weeks 12-30; nerve fibres from the thalamus wait in the subplate (about 14-22 weeks) before growing into the cortex itself (about 23-24 weeks). Whether the subplate can support any experience is exactly what the fetal-pain debate turns on.
Facts Are Important: Understanding and Navigating Viabilitystatement
rates of neonatal survival to discharge at this time range dramatically from 23% to 27% for births at 23 weeks, 42% to 59% for births at 24 weeks, and 67% to 76% for births at 25 weeks of gestation. The consensus also notes that deliveries before 23 weeks have a 5–6% survival rate and that significant morbidity is universal (98–100%) among the rare survivors.
ACOG's own figures, which are older and lower than the newer NICHD data above (e.g. 30% of actively treated 22-weekers in Bell 2022). ACOG also writes: 'While there is no single formally recognized clinical definition of “viability,”' and 'ACOG strongly discourages the inclusion of viability in legislation or regulation.' Both sides agree viability is a moving, hospital-dependent line.
Guide to Language and Abortionstatement
It is clinically inaccurate to use the word “heartbeat” to describe the sound that can be heard on ultrasound in very early pregnancy. In fact, there are no chambers of the heart developed at the early stage in pregnancy that these bills are used to target, so there is no recognizable “heartbeat.” What pregnant people may hear is the ultrasound machine translating electronic impulses that signify fetal cardiac activity into the sound that we recognize as a heartbeat.
ACOG's case against 'heartbeat bill'. Under 'Fetal heartbeat' the guide adds: 'Until the chambers of the heart have been developed, it is not accurate to characterize the embryo or fetus’s cardiac development as a heartbeat', and recommends '“Embryonic cardiac activity” before ten completed weeks of gestation and “fetal cardiac activity” after ten completed weeks of gestation'. The guide is advocacy as well as terminology: on the same page it calls abortion 'a part of comprehensive health care' and rejects 'baby' and 'unborn child'.
Can fetuses feel pain?paper
Avoiding a discussion of fetal pain with women requesting abortions is not misguided paternalism21 but a sound policy based on good evidence that fetuses cannot experience pain.
Derbyshire's earlier view (the '21' is a reference number in the original). He argued pain needs conscious, learned content that a fetus cannot have, while also writing that 'good evidence exists that the biological system necessary for pain is intact and functional from around 26 weeks' gestation.' The paper's competing-interests note: 'SWGD has served as an unpaid consultant for Planned Parenthood of Virginia, USA and Planned Parenthood of Wisconsin, USA, and for the Pro-Choice Forum, United Kingdom.'
RCOG Fetal Awareness Evidence Review (conclusions)statement
To date, evidence indicates that the possibility of pain perception before 28 weeks of gestation is unlikely. At present, there is no basis for considering the administration of analgesia or anaesthesia to a fetus before termination of pregnancy in the first or second trimester to prevent fetal perception of pain.
The UK college's current view moved the line later, not earlier: its 2010 report (summarised in the 2022 background) concluded 'that connections from the periphery to the cortex are not intact before 24 weeks of gestation, and thus it was reasonable to conclude that the fetus cannot experience pain in any sense prior to this gestation.' The 2022 review relies on preterm-infant studies: 'the distinction between touch and noxious evoked cortical activity … is not clear until 32–33 weeks'. It also notes 'Healthy fetuses display increasing complex spontaneous facial movements from 24 weeks of gestation' and a 'needle-evoked reflex grimace at 23 weeks'. Its working group included Stuart Derbyshire and the medical directors of the British Pregnancy Advisory Service and MSI Reproductive Choices (both abortion providers).
Fetal pain: a systematic multidisciplinary review of the evidencepaper
Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester.
The review ACOG cites most. Its abstract: 'Thalamocortical fibers begin appearing between 23 to 30 weeks' gestational age, while electroencephalography suggests the capacity for functional pain perception in preterm neonates probably does not exist before 29 or 30 weeks.' It treats withdrawal reflexes and stress hormones as not proving pain because 'they can be elicited by nonpainful stimuli and occur without conscious cortical processing.'
Facts Are Important: Gestational Development and Capacity for Painstatement
The science conclusively establishes that a human fetus does not have the capacity to experience pain until after at least 24–25 weeks. Every major medical organization that has examined this issue and peer-reviewed studies on the matter have consistently reached the conclusion that abortion before this point does not result in the perception of pain in a fetus.
ACOG's position, in an advocacy series. Note what it leans on: its references are the RCOG 2010 report, Lee et al. 2005 and amicus briefs; it does not cite Derbyshire and Bockmann 2020, who wrote 'Arguably, there never was a consensus that fetal pain is not possible before 24 weeks.' 'Conclusively' is stronger than the RCOG's own 2022 wording ('unlikely'). ACOG also says anaesthesia in fetal surgery 'may be appropriate because it serves other purposes unrelated to pain'.
E04 My body, my choice.
E13 The Bible says life begins at first breath.
E23 The fetus can't feel pain and will never know it existed. No one is harmed.
E28 Abortion bans are sending women home mid-miscarriage. Anya Cook's water broke at 16 weeks, the baby was doomed, and the hospital turned her away because of Florida's ban. She nearly bled to death.
E31 Before viability it can't survive without her body, so it's her decision. That's why Roe drew the line at viability.
E43 Nobody kills babies after they're born. That's a lie Trump made up to scare people. Infanticide is already illegal.