Conclusions: At 10-14 weeks' gestation, twin pregnancies with the lambda sign can be classified as dichorionic and pregnancies with absent lambda sign can be ...Clipboard,SearchHistory,andseveralotheradvancedfeaturesaretemporarilyunavailable.SkiptomainpagecontentCOVID-19InformationPublichealthinformation(CDC)Researchinformation(NIH)SARS-CoV-2data(NCBI)Preventionandtreatmentinformation(HHS)Español AccesskeysNCBIHomepageMyNCBIHomepageMainContentMainNavigationSearch:SearchAdvancedClipboardUserGuideSaveEmailSendtoClipboardMyBibliographyCollectionsCitationmanagerDisplayoptionsDisplayoptionsFormatAbstractPubMedPMIDSavecitationtofileFormat:Summary(text)PubMedPMIDAbstract(text)CSVCreatefileCancelEmailcitationSubject:1selecteditem:9052601-PubMedTo:Format:SummarySummary(text)AbstractAbstract(text)MeSHandotherdataSendemailCancelAddtoCollectionsCreateanewcollectionAddtoanexistingcollectionNameyourcollection:Namemustbelessthan100charactersChooseacollection:UnabletoloadyourcollectionduetoanerrorPleasetryagainAddCancelAddtoMyBibliographyMyBibliographyUnabletoloadyourdelegatesduetoanerrorPleasetryagainAddCancelYoursavedsearchNameofsavedsearch:Searchterms:TestsearchtermsWouldyoulikeemailupdatesofnewsearchresults?SavedSearchAlertRadioButtonsYesNoEmail:(change)Frequency:MonthlyWeeklyDailyWhichday?ThefirstSundayThefirstMondayThefirstTuesdayThefirstWednesdayThefirstThursdayThefirstFridayThefirstSaturdayThefirstdayThefirstweekdayWhichday?SundayMondayTuesdayWednesdayThursdayFridaySaturdayReportformat:SummarySummary(text)AbstractAbstract(text)PubMedSendatmost:1item5items10items20items50items100items200itemsSendevenwhentherearen'tanynewresultsOptionaltextinemail:SaveCancelCreateafileforexternalcitationmanagementsoftwareCreatefileCancelYourRSSFeedNameofRSSFeed:Numberofitemsdisplayed:510152050100CreateRSSCancelRSSLinkCopyActionsCiteFavoritesDisplayoptionsDisplayoptionsFormatAbstractPubMedPMIDSharePermalinkCopyPagenavigationTitle&authorsAbstractSimilararticlesCitedbyMeSHtermsRelatedinformation