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مستخدم:Ahmed Aboshama/Fetus

من ويكيبيديا، الموسوعة الحرة

الجنين الحي هو مرحلة في النماء السابق للولادة في الكائنات الولودية. في التطور البشري، الجنين الحي (الجمع: أجنة) هو مرحلة ما قبل الولادة بين مرحلة الجنين والولادة. تميل مرحلة الجنين الحي في التطور البشري أن تبدأ من العمر الحملي 11 أسبوع (9 أسابيع من الإخصاب).[1][2] على أي حال، النماء السابق للولادة هو عملية مستمرة بلا ملامح واضحة للتفريق بين الجنين والجنين الحي. يتميز كذلك الجنين الحي بوجود كل أعضاء الجسم الكبرى، رغم أنها ليس متطورة بالكامل ولا تؤدي وظيفتها على أكمل وجه بل وبعضها حتى ليس في موقعه التشريحي النهائي.

التطور

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الأسابيع 9 لـ 16 (الشهر 2¼ إلى 4)

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حركة الجنين عند 9 أسابيع من العمر الحملي
رأس جنين حي، مرتبطة بالمشيمة، عند حوالي 12 أسبوع بعد الإخصاب. حتى حوالي 9 أسابيع بعد الإخصاب يمكن أن يوصف بأنه جنين.

في البشر، تبدأ مرحلة الجنين الحي في بداية الأسبوع التاسع. في بداية المرحلة، يكونطول الجنين الحي عادة 30 مليمتر (1.2 بوصة) من التاج للردف، ويزن حوالي 8 جرام. تشكل الرأس تقريبًا حوالي نصف حجم الجنين الحي.[3] الحركة المشابهة للتنفس في الجنين الحي ضرورية لتحفيز تطور الرئة وليس للحصول على الأكسجين.[4] يتواجد القلب، واليدان، والقدمان، والمخ، وأعضاء أخرى لكنهم فقط في بداية التطور ولديهم الحد الأدنى من الوظيفة.[5][6] تبدأ الأعضاء التناسلية في التكون وتصبح المشيمة مكتملة الوظيفة خلال الأسبوع 9.[7]

عند تلك النقطة من التطور، تحدث حركات غير منضبطة وارتجافات حيث تبدأ العضلات، والمخ، والمسارات العصبية في التطور.[8]

الأسابيع 17 لـ 25 (الشهور 4¼ إلى 6¼)

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تشعر المرأة الحامل لأول مرة عادة بحركات الجنين الحي عند حوالي 21 أسبوع، بينما تشعر المرأة التي أنجبت من قبل بحركات الجنين بحلول الأسبوع 20.[9] بنهاية الشهر الخامس، يصل طول الجنين لحوالي 20 سم (8 بوصة)

الأسابيع 26 لـ38 (الشهر 6½ لـ 9½)

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وصف فنان لجنين حي بعد 38 أسبوع من الإخصاب، حوالي 51 سم (20 بوصة) من الرأس لإصبع القدم.[10]

تزيد كمية الدهون في الجسم بشكل سريع. لا تكون الرئتان ناضجتين بشكل كامل. تتكون وصلات المهاد في المخ التي تتوسط المدخلات الحسية. العظام تكون متطورة بشكل كامل، لكن لا تزال ناعمة ومرنة. يصبح الحديد، والكالسيوم، والفوسفور أكثر وفرة. تصل الأظافر لنهاية أطراف الأصابع. يبدأ زَغَبُ الجنين (شعر لانوغو) في الاختفاء، حتى يختفي تماما ماعدا على أعلى الذراعين، والكتفين. تظهر براعم ثديية صغيرة في كلا الجنسين. يصبح شعر الرأس أخشن وأكثر سمكًا. تكون الولادة وشيكة وتحدث حول الأسبوع 38 بعد الإخصاب. يعتبر الجنين الحي مكتمل النمو وجاهز للولادة بين الأسبوعين 36 و40، حين يكون جاهزًا بما يكفي للحياة خارج الرحم.[11][12] قد يكون طوله بين 48 لـ53 سم (19 لـ21 بوصة) حين يولد. يكون التحكم في الحركة محدودًا عند الولادة، وتتطور الحركات الإرادية الهادفة حتى البلوغ.[13][14]

التنوع في النمو

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يوجد تنوع كبير في نمو الجنين البشري الحي. حين يكون حجم الجنين الحي أقل من المتوقع، تعرف تلك الحالة باسم نخلف النمو داخل الرحم (Intrauterine growth restriction)، يمكن أن تكون العوامل المؤثرة على نمو الجنين الحي نابعة من الأم، أو المشيمة، أو الجنين.[15]

عوامل أموية تشمل وزن الأم، ومؤشر كتلة الجسم، والحالة الغذائية، والضغط النفسي، والتعرض للسموم (مثل التبغ، والكحول، والهيروين، والأدوية الأخرى الضارة للجنين الحي)، وتدفق الدم الرحمي

عوامل مشيمية تشمل الحجم، والتركيب الدقيق، وتدفق الدم السري، والبروتينات الناقلة والرابطة، واستهلاك وإنتاج المغذيات.

عوامل جنينية تشمل الجينوم الجنيني، وإنتاج المغذيات، والمخرجات الهرمونية. كذلك تميل الأجنة الأنثوية لأن يكون وزنها أقل من الذكور عند الولادة.[15]

يتم تقسيم نمو الجنين عادة كما يلي: صغير بالنسبة لسن الحمل، ومناسب بالنسبة لسن الحمل، وكبير بالنسبة لسن الحمل.[16] قد يؤدي صغير بالنسبة لسن الحمل إلى وزن ولادة منخفض ، رغم أن الولادة المبكرة قد تؤدي كذلك إلى وزن ولادة منخفض. يزيد وزن الولادة المنخفض خطر وفيات الفترة المحيطة بالولادة، والاختناق، وانخفاض درجة الحرارة، وكثرة كريات الدم الحمر، ونقص كالسيوم الدم، واضطرابات مناعية، واضطرابات عصبية، ومشاكل صحية أخرى طويلة الأمد. قد يكون الطفل الصغير بالنسبة لسن الحمل مصحوبًا بتأخر في النمو، أو قد يكون مصحوبًا بالتقزم المطلق للنمو

القابلية للحياة

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Viability refers to a point in fetal development at which the fetus may survive outside the womb. The lower limit of viability is approximately 5-3/4 months gestational age and is usually later.[17]

There is no sharp limit of development, age, or weight at which a fetus automatically becomes viable.[18] According to data from 2003–05, survival rates are 20–35% for babies born at 23 weeks of gestation (5-3/4 months); 50–70% at 24-25 weeks (6 - 6-1/4 months); and >90% at 26-27 weeks (6-1/2 - 6-3/4 months) and over.[19] It is rare for a baby weighing less than 1.1 رطل (0.50 كـغ) to survive.

When such premature babies are born, the main causes of perinatal mortality are that the respiratory system and the central nervous system are not completely differentiated. If given expert postnatal care, some fetuses weighing less than 1.1 رطل (0.50 كـغ) may survive, and are referred to as extremely low birth weight or immature infants.

Preterm birth is the most common cause of perinatal mortality, causing almost 30 percent of neonatal deaths.[19] At an occurrence rate of 5% to 18% of all deliveries,[20] it is also more common than postmature birth, which occurs in 3% to 12% of pregnancies.[21]

جهاز الدوران

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قبل الولادة

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Diagram of the human fetal circulatory system.

The heart and blood vessels which form the circulatory system, form relatively early during embryonic development, but continue to grow and develop in complexity in the growing fetus. A functional circulatory system is a biological necessity, since mammalian tissues can not grow more than a few cell layers thick without an active blood supply. The prenatal circulation of blood is different than the postnatal circulation, mainly because the lungs are not in use. The fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord.[22]

Blood from the placenta is carried to the fetus by the umbilical vein. About half of this enters the fetal ductus venosus and is carried to the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver. The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of the heart. In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows from the right into the left atrium, thus bypassing pulmonary circulation. The majority of blood flow is into the left ventricle from where it is pumped through the aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the woman's circulation.[22]

Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid).[22]

التطور بعد الولادة

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With the first breath after birth, the system changes suddenly. Pulmonary resistance is reduced dramatically, prompting more blood to move into the pulmonary arteries from the right atrium and ventricle of the heart and less to flow through the foramen ovale into the left atrium. The blood from the lungs travels through the pulmonary veins to the left atrium, producing an increase in pressure that pushes the septum primum against the septum secundum, closing the foramen ovale and completing the separation of the newborn's circulatory system into the standard left and right sides. Thereafter, the foramen ovale is known as the fossa ovalis.

The ductus arteriosus normally closes within one or two days of birth, leaving the ligamentum arteriosum, while the umbilical vein and ductus venosus usually closes within two to five days after birth, leaving, respectively, the liver's ligamentum teres and ligamentum venosus.

  • 3D ultrasound of 3 بوصة (76 مـم) fetus (about 3-1/2 months gestational age)
    3D ultrasound of 3 بوصة (76 مـم) fetus (about 3-1/2 months gestational age)
  • Fetus at 4-1/4 months
    Fetus at 4-1/4 months
  • Fetus at 5 months
    Fetus at 5 months

جهاز المناعة

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The placenta functions as a maternal-fetal barrier against the transmission of microbes. When this is insufficient, mother-to-child transmission of infectious diseases can occur.

Maternal IgG antibodies cross the placenta, giving the fetus passive immunity against those diseases for which the mother has antibodies. This transfer of antibodies in humans begins as early as the fifth month (gestational age) and certainly by the sixth month.[23]

مشاكل تنموية

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A developing fetus is highly susceptible to anomalies in its growth and metabolism, increasing the risk of birth defects. One area of concern is the lifestyle choices a pregnant person makes during pregnancy.[24] Diet is especially important in the early stages of development. Studies show that supplementation of the person's diet with folic acid reduces the risk of spina bifida and other neural tube defects. Another dietary concern is whether breakfast is eaten. Skipping breakfast could lead to extended periods of lower than normal nutrients in the pregnant person's blood, leading to a higher risk of prematurity, or other birth defects in the fetus. During this time alcohol consumption may increase the risk of the development of fetal alcohol syndrome, a condition leading to intellectual disability in some infants.[25]

Smoking during pregnancy may also lead to reduced birth weight. Low birth weight is defined as 2500 grams (5.5 lb). Low birth weight is a concern for medical providers due to the tendency of these infants, described as "premature by weight", to have a higher risk of secondary medical problems. Some research shows that fetal ultrasounds (including Doppler, 3D/4D ultrasound and 2D ultrasound) can have some effects on birth weight and neurodevelopment.[26]

Congenital disorders are acquired before birth. Infants with certain congenital heart defects can survive only as long as the ductus remains open: in such cases the closure of the ductus can be delayed by the administration of prostaglandins to permit sufficient time for the surgical correction of the anomalies. Conversely, in cases of patent ductus arteriosus, where the ductus does not properly close, drugs that inhibit prostaglandin synthesis can be used to encourage its closure, so that surgery can be avoided.

Other heart birth defects include ventricular septal defect, pulmonary atresia, and Tetralogy of Fallot.

ألم الجنين

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Fetal pain, its existence and its implications are debated politically and academically. According to the conclusions of a review published in 2005, "Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester."[27][28] However, developmental neurobiologists argue that the establishment of thalamocortical connections (at about 6-1/2 months) is an essential event with regard to fetal perception of pain.[29] Nevertheless, the perception of pain involves sensory, emotional and cognitive factors and it is "impossible to know" when pain is experienced, even if it is known when thalamocortical connections are established.[29] Some authors [30] argue that fetal pain is possible from the second half of pregnancy: “The available scientific evidence makes it possible, even probable, that fetal pain perception occurs well before late gestation” wrote KJS Anand in the journal of the IASP.[31]

Whether a fetus has the ability to feel pain and suffering is part of the abortion debate.[32][33] In the United States, for example, pro-life advocates have proposed legislation that would require providers of abortions to inform pregnant people that their fetuses may feel pain during the procedure and that would require each person to accept or decline anesthesia for the fetus.[34]

القضايا القانونية والاجتماعية

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Abortion of a human pregnancy is legal and/or tolerated in most countries, although with gestational time limits that normally prohibit late-term abortions.[35]

Use of the word fetus has been banned by the government of the United States from publication by the Centers for Disease Control and Prevention.[36][37]

حيوانات أخرى

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Fourteen phases of elephant development before birth

A fetus is a stage in the prenatal development of viviparous organisms. This stage lies between embryogenesis and birth. Many vertebrates have fetal stages, ranging from most mammals to many fish. In addition, some invertebrates bear live young, including some species of onychophora[38] and many arthropods. The prevalence of convergent evolution to the fetal stage shows that it is relatively easy to develop. It presumably originates from a delay of egg release, with the eggs being hatched inside the parent before being laid. Over time, the robustness of the egg wall can be decreased until it becomes little more than a sac.

The fetuses of most mammals are situated similarly to the human fetus within their mothers.[39] However, the anatomy of the area surrounding a fetus is different in litter-bearing animals compared to humans: each fetus of a litter-bearing animal is surrounded by placental tissue and is lodged along one of two long uteri instead of the single uterus found in a human female.

Development at birth varies considerably among animals, and even among mammals. Altricial species are relatively helpless at birth and require considerable parental care and protection. In contrast, precocial animals are born with open eyes, have hair or down, have large brains, and are immediately mobile and somewhat able to flee from, or defend themselves against, predators. Primates are precocial at birth, with the exception of humans.[40]

The duration of gestation in placental mammals varies from 18 days in jumping mice to 23 months in elephants.[41] Generally speaking, fetuses of larger land mammals require longer gestation periods.[41]

fetal stage of a porpoise

The benefits of a fetal stage means that young are more developed when they are born. Therefore, they may need less parental care and may be better able to fend for themselves. However, carrying fetuses exerts costs on the mother, who must take on extra food to fuel the growth of her offspring, and whose mobility and comfort may be affected (especially toward the end of the fetal stage).

In some instances, the presence of a fetal stage may allow organisms to time the birth of their offspring to a favorable season.[38]

انظر أيضًا

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مراجع

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  1. ^ Klossner, N. Jayne, Introductory Maternity Nursing (2005): "The fetal stage is from the beginning of the 9th week after fertilization and continues until birth"
  2. ^ "First Trimester - American Pregnancy Association". americanpregnancy.org. 1 مايو 2012. مؤرشف من الأصل في 2009-04-23. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  3. ^ "Fetal development: MedlinePlus Medical Encyclopedia". www.nlm.nih.gov. مؤرشف من الأصل في 2011-10-27. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  4. ^ Institute of Medicine of the National Academies, Preterm Birth: Causes, Consequences, and Prevention نسخة محفوظة 2011-06-07 على موقع واي باك مشين. (2006), page 317. Retrieved 2008-03-12
  5. ^ The Columbia Encyclopedia نسخة محفوظة 2007-10-12 على موقع واي باك مشين. (Sixth Edition). Retrieved 2007-03-05.
  6. ^ Greenfield, Marjorie. “Dr. Spock.com نسخة محفوظة 2007-01-22 على موقع واي باك مشين.". Retrieved 2007-01-20.
  7. ^ "9 Weeks Pregnant – Symptoms, Fetal Development, Tips". مؤرشف من الأصل في 2016-08-16. اطلع عليه بتاريخ 2016-07-21. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  8. ^ Prechtl, Heinz. "Prenatal and Early Postnatal Development of Human Motor Behavior" in Handbook of brain and behaviour in human development, Kalverboer and Gramsbergen eds., pp. 415-418 (2001 Kluwer Academic Publishers): "The first movements to occur are sideward bendings of the head....At 9-10 weeks postmestrual age complex and generalized movements occur. These are the so-called general movements (Prechtl et al., 1979) and the startles. Both include the whole body, but the general movements are slower and have a complex sequence of involved body parts, while the startle is a quick, phasic movement of all limbs and trunk and neck."
  9. ^ Levene, Malcolm et al. Essentials of Neonatal Medicine (Blackwell 2000), p. 8. Retrieved 2007-03-04.
  10. ^ "Fetal development - 40 weeks". BabyCenter. 2015. مؤرشف من الأصل في 2015-08-29. اطلع عليه بتاريخ 2015-08-26. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  11. ^ Your Pregnancy: 36 Weeks نسخة محفوظة 2007-06-01 على موقع واي باك مشين. BabyCenter.com Retrieved June 1, 2007.
  12. ^ "full-term" defined by Memidex/WordNet.
  13. ^ Stanley, Fiona et al. "Cerebral Palsies: Epidemiology and Causal Pathways", page 48 (2000 Cambridge University Press): "Motor competence at birth is limited in the human neonate. The voluntary control of movement develops and matures during a prolonged period up to puberty...."
  14. ^ Becher, Julie-Claire. "Insights into Early Fetal Development". مؤرشف من الأصل في 2013-06-01. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة), Behind the Medical Headlines (Royal College of Physicians of Edinburgh and Royal College of Physicians and Surgeons of Glasgow October 2004)
  15. ^ ا ب Holden, Chris and MacDonald, Anita. Nutrition and Child Health (Elsevier 2000). Retrieved 2007-03-04.
  16. ^ Queenan, John. Management of High-Risk Pregnancy (Blackwell 1999). Retrieved 2007-03-04.
  17. ^ Halamek, Louis. "Prenatal Consultation at the Limits of Viability نسخة محفوظة 2009-06-08 على موقع واي باك مشين.", NeoReviews, Vol.4 No.6 (2003): "most neonatologists would agree that survival of infants younger than approximately 22 to 23 weeks’ estimated gestational age [i.e. 20 to 21 weeks' estimated fertilization age] is universally dismal and that resuscitative efforts should not be undertaken when a neonate is born at this point in pregnancy."
  18. ^ Moore, Keith and Persaud, T. The Developing Human: Clinically Oriented Embryology, p. 103 (Saunders 2003).
  19. ^ ا ب March of Dimes - Neonatal Death نسخة محفوظة 2014-10-24 على موقع واي باك مشين., retrieved September 2, 2009.
  20. ^ World Health Organization (نوفمبر 2014). "Preterm birth Fact sheet N°363". who.int. مؤرشف من الأصل في 7 مارس 2015. اطلع عليه بتاريخ 6 مارس 2015. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  21. ^ Buck، Germaine M.؛ Platt، Robert W. (2011). Reproductive and perinatal epidemiology. Oxford: Oxford University Press. ص. 163. ISBN:9780199857746. مؤرشف من الأصل في 2016-08-15. {{استشهاد بكتاب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  22. ^ ا ب ج Whitaker, Kent. Comprehensive Perinatal and Pediatric Respiratory Care (Delmar 2001). Retrieved 2007-03-04.
  23. ^ Page 202 of Pillitteri, Adele (2009). Maternal and Child Health Nursing: Care of the Childbearing and Childrearing Family. Hagerstwon, MD: Lippincott Williams & Wilkins. ISBN:1-58255-999-6.
  24. ^ Dalby، JT (1978). "Environmental effects on prenatal development". Journal of Pediatric Psychology. ج. 3: 105–109. DOI:10.1093/jpepsy/3.3.105.
  25. ^ Streissguth, Ann Pytkowicz (1997). Fetal alcohol syndrome: a guide for families and communities. Baltimore, MD: Paul H Brookes Pub. ISBN:1-55766-283-5.
  26. ^ "Questions about Prenatal Ultrasound and the Alarming Increase in Autism - Midwifery Today". midwiferytoday.com. 1 ديسمبر 2016. مؤرشف من الأصل في 2012-05-06. {{استشهاد ويب}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة)
  27. ^ Lee، Susan؛ Ralston، HJ؛ Drey، EA؛ Partridge، JC؛ Rosen، MA (24–31 أغسطس 2005). "Fetal Pain A Systematic Multidisciplinary Review of the Evidence". Journal of the American Medical Association. American Medical Association. ج. 294 ع. 8: 947–54. DOI:10.1001/jama.294.8.947. PMID:16118385. مؤرشف من الأصل في 2008-01-10. اطلع عليه بتاريخ 2008-02-14. {{استشهاد بدورية محكمة}}: الوسيط غير المعروف |deadurl= تم تجاهله (مساعدة) Two authors of the study published in JAMA did not report their abortion-related activities, which pro-life groups called a conflict of interest; the editor of JAMA responded that JAMA probably would have mentioned those activities if they had been disclosed, but still would have published the study. See Denise Grady, “Study Authors Didn't Report Abortion Ties” نسخة محفوظة 2009-04-25 على موقع واي باك مشين., New York Times (2005-08-26).
  28. ^ "Study: Fetus feels no pain until third trimester" نسخة محفوظة 2008-03-18 على موقع واي باك مشين. MSNBC
  29. ^ ا ب Johnson, Martin and Everitt, Barry. Essential reproduction (Blackwell 2000): "The multidimensionality of pain perception, involving sensory, emotional, and cognitive factors may in itself be the basis of conscious, painful experience, but it will remain difficult to attribute this to a fetus at any particular developmental age." Retrieved 2007-02-21.
  30. ^ Glover V. The fetus may feel pain from 20 weeks. Conscience. 2004-2005 Winter;25(3):35-7
  31. ^ http://www.iasp-pain.org/AM/AMTemplate.cfm?Section=HOME&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=15390&SECTION=HOME نسخة محفوظة 2013-07-01 على موقع واي باك مشين.
  32. ^ White, R. Frank. " [[New research has discovered that unborn babies can feel pain. "The neural pathways are present for pain to be experienced quite early by unborn babies,” explains Steven Calvin, M.D., perinatologist, chair of the Program in Human Rights Medicine, University of Minnesota, where he teaches obstetrics." [1]]http://www.asahq.org/Newsletters/2001/10_01/white.htm Are We Overlooking Fetal Pain and Suffering During Abortion?] نسخة محفوظة 2016-07-19 على موقع واي باك مشين.", American Society of Anesthesiologists Newsletter (October 2001). Retrieved 2007-03-10.
  33. ^ David, Barry & and Goldberg, Barth. "Recovering Damages for Fetal Pain and Suffering نسخة محفوظة 2007-09-28 على موقع واي باك مشين.", Illinois Bar Journal (December 2002). Retrieved 2007-03-10.
  34. ^ Weisman, Jonathan. "House to Consider Abortion Anesthesia Bill نسخة محفوظة 2008-10-28 على موقع واي باك مشين.", Washington Post 2006-12-05. Retrieved 2007-02-06.
  35. ^ Anika Rahman, Laura Katzive and Stanley K. Henshaw. "A Global Review of Laws on Induced Abortion, 1985-1997 نسخة محفوظة 2016-03-03 على موقع واي باك مشين.", International Family Planning Perspectives Volume 24, Number 2 (June 1998).
  36. ^ CDC banned words include 'diversity', 'transgender' and 'fetus' – report نسخة محفوظة 2017-12-16 على موقع واي باك مشين.. theguardian.com. Accessed 12-16-2017.
  37. ^ CDC gets list of forbidden words: Fetus, transgender, diversity نسخة محفوظة 2017-12-17 على موقع واي باك مشين.. washingtonpost.com. Accessed 12-16-2017.
  38. ^ ا ب Campiglia, Sylvia S.؛ Walker، Muriel H. (1995). "Developing embryo and cyclic changes in the uterus ofPeripatus (Macroperipatus) acacioi (Onychophora, Peripatidae)". Journal of Morphology. ج. 224 ع. 2: 179–198. DOI:10.1002/jmor.1052240207.
  39. ^ ZFIN, Pharyngula Period (24-48 h) نسخة محفوظة 2007-07-14 على موقع واي باك مشين.. Modified from: Kimmel et al., 1995. Developmental Dynamics 203:253-310. Downloaded 5 March 2007.
  40. ^ Lewin, Roger. Human Evolution, page 78 (Blackwell 2004).
  41. ^ ا ب Sumich, James and Dudley, Gordon. Laboratory and Field Investigations in Marine Life, page 320 (Jones & Bartlett 2008).

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