Ultrasound screening for fetal microcephaly following Zika virus exposure







The practice of medicine continues to evolve, and individual circumstances will vary. This publication reflects information available at the time of its submission for publication and is neither designed nor intended to establish an exclusive standard of perinatal care. This publication is not expected to reflect the opinions of all members of the Society for Maternal-Fetal Medicine.



Microcephaly is a condition in which the size of the head is smaller than expected for age. This condition in fetuses and infants has been associated with the recent outbreak of Zika virus. Due to this association, the Centers for Disease Control and Prevention (CDC), American Congress of Obstetricians and Gynecologists (ACOG), and Society for Maternal-Fetal Medicine (SMFM) have suggested prenatal ultrasound evaluation for fetal microcephaly in pregnant women who have been infected or potentially exposed. However, the diagnosis of microcephaly by prenatal sonography is not always straightforward. Given the complexity of prenatal diagnosis of microcephaly, the purpose of this document is to review the ultrasound criteria for the diagnosis following exposure to the Zika virus.


Various national and international agencies have recommended prenatal ultrasound for evaluation for fetal microcephaly in women who have travelled to any of the high-risk areas for Zika exposure during pregnancy. At present, however, there are limited data available regarding criteria for diagnosis of fetal microcephaly in the setting of Zika infection or exposure. In addition, the natural history of fetal microcephaly associated with Zika virus is unknown; although recent reports describe cases of microcephaly after maternal infection. In most cases, it is difficult to differentiate between constitutionally small head size vs pathologic microcephaly, and available data regarding prenatal diagnosis of microcephaly are based on small numbers of cases of varying etiologies.


In cases in which the fetal head circumference (HC) measures >2SD below the mean, we recommend that a detailed neurosonographic examination be performed, as some fetuses with HC >2SD below the mean due to in utero infection will have findings such as periventricular and intraparenchymal echogenic foci, ventriculomegaly, cerebellar hypoplasia, microcephaly, and cortical abnormalities. In addition, assessment of the profile can be helpful as the forehead is often sloping in pathologic microcephaly, and demonstration of this finding should increase the index of suspicion. We recommend that isolated fetal microcephaly should be defined as fetal HC ≥3SD below the mean for gestational age ( Table ), and the diagnosis of pathologic microcephaly is considered certain when the fetal HC is ≥5SD. If the HC by prenatal ultrasound is >2SD below the mean, a careful evaluation of the fetal intracranial anatomy is indicated. If the intracranial anatomy is normal, we recommend follow-up ultrasound in 3-4 weeks.



Table

Means and SD of head circumference as function of gestational age






































































































































































































Gestational age, wk Mean, mm Head circumference, mm: SD below mean
–1 –2 –3 –4 –5
20 175 160 145 131 116 101
21 187 172 157 143 128 113
22 198 184 169 154 140 125
23 210 195 180 166 151 136
24 221 206 191 177 162 147
25 232 217 202 188 173 158
26 242 227 213 198 183 169
27 252 238 223 208 194 179
28 262 247 233 218 203 189
29 271 257 242 227 213 198
30 281 266 251 236 222 207
31 289 274 260 245 230 216
32 297 283 268 253 239 224
33 305 290 276 261 246 232
34 312 297 283 268 253 239
35 319 304 289 275 260 245
36 325 310 295 281 266 251
37 330 316 301 286 272 257
38 335 320 306 291 276 262
39 339 325 310 295 281 266
40 343 328 314 299 284 270
41 346 331 316 302 287 272
42 348 333 319 304 289 275

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

May 4, 2017 | Posted by in GYNECOLOGY | Comments Off on Ultrasound screening for fetal microcephaly following Zika virus exposure

Full access? Get Clinical Tree

Get Clinical Tree app for offline access