|Embryology - 21 Jul 2019 Expand to Translate|
Ultrasound Image of an early Fetus (12 week)
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Some Recent Findings
In this study, we aimed to compare serum 25(OH)D levels in women with and without gestational diabetes mellitus (GDM), and to identify the serum 25(OH)D levels associated with GDM. We recruited 40 women with GDM and 40 healthy pregnant women, aged 20-40 years and in the second trimester, at Gulhane Education and Research Hospital. We excluded women with chronic diseases, preeclampsia, pre-GDM, multiple pregnancies, and those taking medications related to calcium or vitamin D metabolism. We took anthropometric measurements and blood samples during the second trimester. Of the 80 pregnant women, pre-pregnancy body mass index was significantly higher among the GDM group than the healthy group (26.4 ± 5.73 kg/m2 vs. 22.6 ± 3.56 kg/m2, p = .001). Serum 25(OH)D levels in women with GDM were significantly lower than those in healthy women (16.8 ± 9.90 ng/mL vs. 20.9 ± 8.16 ng/mL, p = .016). The prevalence of severe vitamin D deficiency was as high as 72.5% among women in the GDM group, with a 1.74-fold increased risk of deficient status. Levels of 25(OH)D lower than a cutoff value of 14.0 ng/mL were determined to be related to GDM. These study results suggest that maternal vitamin D deficiency in mid-pregnancy is significantly associated with development of GDM."
|More recent papers|
This table allows an automated computer search of the external PubMed database using the listed "Search term" text link.
Search term: Second Trimester
|These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.
Three-dimensional reconstruction of the lateral (top row) and medial (bottom row) surface of second trimester (13 to 21 week) brains to reveal the development of the Sylvian fissure or lateral sulcus (green arrow), the calcarine fissure (blue arrow), and the parieto-occipital sulcus (red arrow), respectively.
The images below are from a recent MRI study of fixed fetal brains at different weeks of development during the second trimester.
- Links: Neural System - Fetal
Second Trimester Timeline
|Fertilisation Age FA||Gestational Age GA|
|14|| Week 12 - CRL 85 mm, femur length 15 mm, biparietal diameter 25 mm
Hearing Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic space) around membranous labrynth and fills with perilymph
Genital male and female external genital differences observable
Respiratory Month 3-6 - lungs appear glandular, end month 6 alveolar cells type 2 appear and begin to secrete surfactant
Tongue Week 12 - first differentiated epithelial cells (Type II and III)
Genital female genital canal (80 days) formed with absorption of the median septum
|15||Tongue Week 12 to 13 - maximum synapses between cells and afferent nerve fibers
Hearing - Outer Ear Development Week 13 - Meatal plug disc-like, innermost surface in contact with the primordial malleus, contributes to the formation of the tympanic membrane.
|16||Tongue Week 14 to 15 - taste pores develop, mucous
Ovary Development 100 days - primary follicles present
Nail Development toenails appear
Head Development facial skeleton remodelling begins
|17||Pancreas glucagon detectable in fetal plasma.|
|18|| Hearing Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone. Continues to ossify to form mastoid process of temporal bone.
Pituitary adenohypophysis fully differentiated
Respiratory Week 16 to 25 lung histology - canalicular
Hearing - Outer Ear Development Week 16.5 - External auditory meatus is fully patent throughout its length, lumen is still narrow and curved.
Skin 4 months - basal cell- proliferation generates folds in basement membrane; neural crest cells- (melanocytes) migrate into epithelium; embryonic connective tissue- differentiates into dermis, a loose ct layer over a dense ct layer. Beneath the dense ct layer is another loose ct layer that will form the subcutaneous layer. Ectoderm contributes to nails, hair follictles and glands. Nails form as thickening of ectoderm epidermis at the tips of fingers and toes. These form germinative cells of nail field. Cords of these cells extend into mesoderm forming epithelial columns. These form hair follocles, sebaceous and sweat glands.
primary follicles begin to form in the ovary and are characterized by an oocyte
glandular urethra forms and skin folds present
|19||Neural - Brain development histology week 17|
|20||Tongue Week 18 - substance P detected in dermal papillae, not in taste bud primordia
Skin vernix caseosa covers skin
Spleen Week 18 - alpha-SMA-positive reticulum cells increase in number and began to form a reticular framework. An accumulation of T and B lymphocytes occurred within the framework, and a primitive white pulp was observed around the arterioles. 
Hearing - Outer Ear Development week 18 - External auditory meatus is already fully expanded to its complete form.
|22||Pituitary week 20 to 24 growth hormone levels peak, then decline
Skin lanugo, skin hair
Skin 5 months - Hair growth initiated at base of cord, lateral outgrowths form associated sebaceous glands; Other cords elongate and coil to form sweat glands; Cords in mammary region branch as they elongate to form mammary glands.
|24|| Neural brain cortical sulcation - sylvian fissure, interhemispheric fissure, callosal sulcus, parietooccipital fissure, and hippocampic fissures present
Spleen - Week 22 - antigenic diversity of the reticular framework was observed, and T and B lymphocytes were segregated in the framework. T lymphocytes were sorted into the alpha-smooth muscle actin-positive reticular framework, and the periarteriolar lymphoid sheath (PALS) was formed around the arteriole. B lymphocytes aggregated in eccentric portions to the PALS and formed the lymph follicle (LF). The reticular framework of the LF was alpha-SMA-negative. 
|26||Respiratory Week 24 to 40 lung histology - terminal sac
Earliest potential survival expected if born
ovarian follicles can consist of growing oocytes surrounded by several layers of granulosa cells
|27||Respiratory end month 6 alveolar cells type 2 appear and begin to secrete surfactant|
- Nunthapiwat S, Sekararithi R, Wanapirak C, Sirichotiyakul S, Tongprasert F, Srisupundit K, Luewan S & Tongsong T. (2019). Second Trimester Serum Biomarker Screen for Fetal Aneuploidies as a Predictor of Preterm Delivery: A Population-Based Study. Gynecol. Obstet. Invest. , , 1-8. PMID: 30602167 DOI.
- Ede G, Keskin U, Cemal Yenen M & Samur G. (2019). Lower vitamin D levels during the second trimester are associated with developing gestational diabetes mellitus: an observational cross-sectional study. Gynecol. Endocrinol. , , 1-4. PMID: 30599810 DOI.
- Akhter N & Chakraborty RK. (2014). Second trimester sonographic features of fetal chromosomal defects. Mymensingh Med J , 23, 412-6. PMID: 24858178
- Savasan ZA, Goncalves LF & Bahado-Singh RO. (2014). Second- and third-trimester biochemical and ultrasound markers predictive of ischemic placental disease. Semin. Perinatol. , 38, 167-76. PMID: 24836829 DOI.
- Report of the Workshop on Acute Perinatal Asphyxia in Term Infants, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, National Institute of Child Health and Human Development, NIH Publication No. 96-3823, March 1996.
- Huang H, Xue R, Zhang J, Ren T, Richards LJ, Yarowsky P, Miller MI & Mori S. (2009). Anatomical characterization of human fetal brain development with diffusion tensor magnetic resonance imaging. J. Neurosci. , 29, 4263-73. PMID: 19339620 DOI.
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Cite this page: Hill, M.A. (2019, July 21) Embryology Second Trimester. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Second_Trimester
- © Dr Mark Hill 2019, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G