HUHUMAN DEVELOPMENT BEFORE BIRTH!
HUMAN DEVELOPMENT BEFORE BIRTH
Z1*L+&+=Q!)*L(+$!&2!=%+=*-2(%+!K(2.!2.*!@+(%+!%4!&!3&+N$!$-*13!&+6!&!K%3&+N$!
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%4!&!+*K!(+6('(6@&#N$!=%3-#*2*!L*+*2(=!=%6*:!!b*+6*1?!*Q*!=%#%1?!&+6!%2.*1!21&(2$!
&1*!6*2*13(+*6!&2!=%+=*-2(%+:!
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&13$!&+6!#*L$!&1*!*$2&)#($.*6!)Q!&)%@2!4%@1!K**>$!&42*1!=%+=*-2(%+:!!7(L.2!K**>$!
&42*1!=%+=*-2(%+?!*\=*-2!4%1!2.*!$3&##!$(c*?!2.*!6*'*#%-(+L!.@3&+N$!%'*1&##!
&--*&1&+=*!&+6!3&+Q!(+2*1+&#!$21@=2@1*$!=#%$*#Q!1*$*3)#*!2.*!+*K)%1+:!
Z1*L+&+=Q!($!+%2!W@$2!&!2(3*!4%1!L1%K(+L!&##!2.*!-&12$!%4!2.*!)%6Q:!_2!($!&#$%!&!2(3*!
%4!-1*-&1&2(%+!4%1!$@1'('&#!&42*1!)(12.:!]&+Q!=%33%+!6&(#Q!&=2('(2(*$!$**+!(+!
=.(#61*+!&+6!&6@#2$!)*L(+!(+!2.*!K%3)d$2&12(+L!3%1*!2.&+!e9!K**>$!before!)(12.:!
B.*$*!&=2('(2(*$!(+=#@6*!.(==@-$?!2%@=.(+L!2.*!4&=*?!)1*&2.(+L!3%2(%+$?!@1(+&2(%+?!
1(L.2D!%1!#*42D.&+6*6+*$$?!2.@3)!$@=>(+L?!$K&##%K(+L?!Q&K+(+L?!W&K!3%'*3*+2?!
1*4#*\*$?!O7]!$#**-?!.*&1(+L?!2&$2*?!$*+$&2(%+?!&+6!$%!%+:!!!
f+#*$$!%2.*1K($*!+%2*6?!&##!-1*+&2&#!&L*$!(+!2.*!1*$2!%4!2.($!L@(6*!&1*!1*4*1*+=*6!
41%3!2.*!$2&12!%4!2.*!#&$2!+%13&#!3*+$21@&#!-*1(%6:!B.($!&L*!($!2K%!K**>$!L1*&2*1!
2.&+!2.*!&L*!$(+=*!=%+=*-2(%+:!
The First Two Weeks
,.%12#Q!&42*1!&!K%3&+N$!-*1(%6!)*L(+$?!.*1!)%6Q!)*L(+$!-1*-&1(+L!4%1!2.*!
-%$$()(#(2Q!%4!-1*L+&+=Q:!!
"--1%\(3&2*#Q!A!K**>$!(+2%!.*1!=Q=#*?!&!K%3&+!1*#*&$*$!&+!*LL!41%3!%+*!%4!.*1!
%'&1(*$!(+2%!&!G&##%-(&+!2@)*:!a%+=*-2(%+!($!+%K!-%$$()#*!4%1!2.*!+*\2!AF!.%@1$!%1!
$%!&+6!$(L+(4(*$!2.*!)*L(++(+L!%4!-1*L+&+=Q:!
"42*1!=%+=*-2(%+?!2.*!$(+L#*D=*##!*3)1Q%!.&$!&!6(&3*2*1!%4!&--1%\(3&2*#Q!F!
2.%@$&+62.$!%4!&+!(+=.:!
2 to 4 Weeks
B.*!=*##$!%4!2.*!*3)1Q%!1*-*&2*6#Q!6('(6*!3%'(+L!2.1%@L.!2.*!G&##%-(&+!2@)*!(+2%!
#
2.*!K%3&+N$!@2*1@$!%1!K%3):!_3-#&+2&2(%+?!2.*!-1%=*$$!K.*1*)Q!2.*!@+)%1+!=.(#6!
*3)*6$!(2$*#4!(+2%!2.*!K&##!%4!2.*!K%3)?!)*L(+$!)Q!2.*!*+6!%4!2.*!2.(16!K**>!&+6!($!
=%3-#*2*6!6@1(+L!2.*!4%@12.!K**>!%4!-1*L+&+=Q:
4 to 6 Weeks!
"2!F!K**>$?!2.*!@+)%1+!=.(#6!($!#*$$!
2.&+!8`8992.!%4!&+!(+=.!#%+L:!
RQ!I!K**>$?!6*'*#%-3*+2!%4!2.*!)1&(+?!
$-(+&#!=%16?!&+6!.*&12!($!K*##!
@+6*1K&Q:!!
B.*!.*&12!)*L(+$!)*&2(+L!&2!I!K**>$!
&+6!%+*!6&Q!&+6!($!'($()#*!)Q!
@#21&$%@+6!&#3%$2!(33*6(&2*#Q:!!
!
6 to 8 Weeks
!
RQ!C!K**>$?!2.*!.*&12!($!-@3-(+L!2.*!
@+)%1+!=.(#6N$!%K+!)#%%6!2%!.($!%1!.*1!
)1&(+!&+6!)%6Q:!!
"##!4%@1!=.&3)*1$!%4!2.*!.*&12!&1*!
-1*$*+2?!&+6!3%1*!2.&+!8!3(##(%+!
.*&12)*&2$!.&'*!%==@11*6:!
B.*!.*&6?!=.*$2?!&+6!&)6%3(+&#!=&'(2(*$!.&'*!4%13*6!&+6!2.*!)*L(++(+L$!%4!2.*!
&13$!&+6!#*L$!&1*!*&$(#Q!$**+:!
$
"2!C!K**>$?!2.*!@+)%1+!=.(#6!3*&$@1*$!#*$$!2.&+!g!%4!&+!(+=.!#%+L!41%3!.*&6!2%!
1@3-:!
O&-(6!)1&(+!6*'*#%-3*+2!=%+2(+@*$!K(2.!2.*!&--*&1&+=*!%4!2.*!=*1*)1&#!
.*3($-.*1*$!&2!Ch!K**>$:!
B.*!@+)%1+!=.(#6!1*4#*\('*#Q!2@1+$!&K&Q!(+!1*$-%+$*!2%!#(L.2!2%@=.!%+!2.*!4&=*!&2!
Eh!K**>$:!!
G(+L*1$!&1*!)*L(++(+L!2%!4%13!%+!2.*!.&+6:!!
8 to 10 Weeks!
B.*!@+)%1+!=.(#6!($!&)%@2!h!(+=.!
41%3!.*&6!2%!1@3-:!
!
RQ!Hh!K**>$?!)%+*$!%4!2.*!W&K!&+6!
=%##&1)%+*!)*L(+!2%!.&16*+:!!
R1&(+K&'*$!.&'*!)**+!3*&$@1*6!&+6!
1*=%16*6!)*4%1*!Hh!K**>$:!
RQ![!K**>$?!2.*!.&+6$!3%'*?!2.*!+*=>!2@1+$?!&+6!.(==@-$!)*L(+:!
b(1#$!+%K!.&'*!%'&1(*$!&+6!)%Q$!.&'*!2*$2*$:!
B.*!@+)%1+!=.(#6N$!.*&12!1&2*!-*&>$!&2!&)%@2!8E9!)*&2$!-*1!3(+@2*!&+6!K(##!
L1&6@&##Q!$#%K!6%K+!@+2(#!)(12.:!!
7#*=21(=&#!1*=%16(+L$!%4!2.*!.*&12!&2![h!K**>$!&1*!'*1Q!$(3(#&1!2%!2.*!7/b!21&=(+L!
%4!2.*!+*K)%1+:!B.*!.*&12!($!+*&1#Q!4@##Q!4%13*6:!!
!
!
!
%
!
10 to 12 Weeks!
RQ!89!K**>$!(+2*13(22*+2!)1*&2.(+L!
3%2(%+$!)*L(+?!&+6!>(6+*Q$!)*L(+!2%!
-1%6@=*!&+6!1*#*&$*!@1(+*:!"##!4(+L*1$!
&+6!2%*$!&1*!41**!&+6!4@##Q!4%13*6?!
&+6!$*'*1&#!.@+61*6!3@$=#*$!&1*!
-1*$*+2:!!!
B.*!.&+6$!&+6!4**2!3%'*!41*^@*+2#Q?!
&+6!3%$2!@+)%1+!=.(#61*+!$.%K!4(1$2!
$(L+$!%4!1(L.2D!%1!#*42D.&+6*6+*$$:!!
Z&(+!1*=*-2%1$!(+!2.*!$>(+?!2.*!$*+$%1Q!+*1'*$!=%++*=2(+L!2.*3!2%!2.*!$-(+&#!=%16?!
&+6!2.*!+*1'*!21&=2$!(+!2.*!$-(+&#!=%16!2.&2!K(##!=&11Q!-&(+!(3-@#$*$!2%!2.*!)1&(+!&1*!
&##!-1*$*+2!)Q!89!K**>$:!
7\-*12$!*$2(3&2*!2.*!89DK**>!@+)%1+!=.(#6!-%$$*$$*$!&--1%\(3&2*#Q![9i!%4!2.*!
F?I99!)%6Q!-&12$!4%@+6!(+!&6@#2$:!B.($!3*&+$!&--1%\(3&2*#Q!F?999!-*13&+*+2!
)%6Q!-&12$!&1*!-1*$*+2!W@$2!*(L.2!K**>$!&42*1!=%+=*-2(%+:!_+=1*6()#Q?!2.($!.(L.#Q!
=%3-#*\!@+)%1+!=.(#6!K*(L.$!&)%@2!8`892.!%4!&+!%@+=*!&+6!3*&$@1*$!$#(L.2#Q!#*$$!
2.&+!8g!(+=.*$!41%3!.*&6!2%!1@3-:!
B.*!*Q*#(6$!&1*!2*3-%1&1(#Q!4@$*6!2%L*2.*1!)Q!89h!K**>$:!!
RQ!88!K**>$!2.*!.*&6!3%'*$!4%1K&16!&+6!)&=>?!2.*!W&K!&=2('*#Q!%-*+$!&+6!=#%$*$?!
&+6!2.*!@+)%1+!=.(#6!-*1(%6(=&##Q!$(L.$!&+6!$21*2=.*$:!B.*!4&=*?!-&#3$!%4!2.*!
.&+6$?!&+6!$%#*$!%4!2.*!4**2!&1*!$*+$(2('*!2%!#(L.2!2%@=.:!!!
B.@3)!$@=>(+L!&+6!$K&##%K(+L!&3+(%2(=!4#@(6!)*L(+:!
b(1#$N!%'&1(*$!+%K!=%+2&(+!1*-1%6@=2('*!=*##$!2.&2!K(##!L('*!1($*!2%!*LL$!#&2*1!(+!
#(4*:!"#$%!(+!L(1#$?!2.*!@2*1@$!($!+%K!-1*$*+2:!!!!!
S&K+(+L!)*L(+$!&2!88h!K**>$:!
&
12 to 14 Weeks!
B.*!8ADK**>!@+)%1+!=.(#6!K*(L.$!#*$$!
2.&+!8!%@+=*!&+6!3*&$@1*$!&)%@2!e!
(+=.*$!41%3!.*&6!2%!.**#:!
G(+L*1-1(+2$!$2&12!4%13(+L!K.(#*!
4(+L*1+&(#$!&+6!2%*+&(#$!)*L(+!2%!L1%K:!!
B.*!)%+*$!&1*!.&16*+(+L!(+!3&+Q!
#%=&2(%+$:!
B.*!.*&12)*&2!=&+!)*!6*2*=2*6!K(2.!&!0%--#*1!T&!.&+6D.*#6!@#21&$%@+6!21&+$6@=*1!
@$*6!2%!6*2*=2!2.*!$%@+6$!%4!&+!@+)%1+!=.(#6N$!.*&12U!%1!*\2*1+&#!.*&12!1&2*!3%+(2%1:!!
RQ!8e!K**>$!2.*!#(-$!&+6!+%$*!&1*!4@##Q!4%13*6!&+6!2.*!@+)%1+!=.(#6!=&+!3&>*!
=%3-#*\!4&=(&#!*\-1*$$(%+$:!
14 to 16 Weeks
"2!8F!K**>$?!2.*!@+)%1+!=.(#6!K*(L.$!
&)%@2!A!%@+=*$!&+6!3*&$@1*$!$#(L.2#Q!
#*$$!2.&+!I!(+=.*$!41%3!.*&6!2%!.**#:!
B&$2*!)@6$!&1*!-1*$*+2!&##!%'*1!2.*!
3%@2.!&+6!2%+L@*:!
B.*!@+)%1+!=.(#6!+%K!-1%6@=*$!&!K(6*!
'&1(*2Q!%4!.%13%+*$:!!
"13$!1*&=.!4(+&#!-1%-%12(%+!2%!)%6Q!$(c*:!
RQ!8I!K**>$!2.*!*+2(1*!@+)%1+!=.(#6!T*\=*-2!4%1!-&12$!%4!2.*!$=&#-U!1*$-%+6$!2%!
#(L.2!2%@=.:!B%%2.!6*'*#%-3*+2!($!@+6*1K&Q:
'
16 to 18 Weeks!
"2!8C!K**>$?!2.*!@+)%1+!=.(#6!K*(L.$!
&)%@2!F!%@+=*$!&+6!3*&$@1*$!$#(L.2#Q!
#*$$!2.&+!E!(+=.*$!41%3!.*&6!2%!.**#:!
"!-1*L+&+2!K%3&+!3&Q!)*L(+!2%!4**#!
2.*!@+)%1+!=.(#6!3%'*!&2!8C!K**>$:!
B.*!@+)%1+!=.(#6!)*L(+$!3&>(+L!
$*'*1&#!6(L*$2('*!*+cQ3*$:!
"1%@+6!8E!K**>$!)#%%6!=*##!4%13&2(%+!3%'*$!2%!(2$!-*13&+*+2!#%=&2(%+!(+$(6*!2.*!
)%+*!3&11%K!&+6!2.*!@+)%1+!=.(#6!)*L(+$!$2%1(+L!*+*1LQ!(+!2.*!4%13!%4!)%6Q!4&2:!
18 to 20 Weeks!
RQ!8H!K**>$!4%13&2(%+!%4!2.*!
)1*&2.(+L!-&$$&L*$?!=&##*6!2.*!
)1%+=.(&#!21**?!($!=%3-#*2*:!B.*!
@+)%1+!=.(#6!1*#*&$*$!$21*$$!.%13%+*$!
(+!1*$-%+$*!2%!)*(+L!-%>*6!K(2.!&!
+**6#*:!
"2!8H!K**>$?!2.*!@+)%1+!=.(#6!K*(L.$!
&1%@+6!C!%@+=*$!&+6!3*&$@1*$!&)%@2!H!
(+=.*$!41%3!.*&6!2%!.**#:!
RQ!8[!K**>$?!2.*!.*&12!.&$!)*&2*+!3%1*!2.&+!A9!3(##(%+!2(3*$:
(
20 to 22 Weeks
RQ!A9!K**>$!+*&1#Q!&##!%1L&+$!&+6!
$21@=2@1*$!.&'*!)**+!4%13*6:!
B.*!A9DK**>!@+)%1+!=.(#6!K*(L.$!
&)%@2![!%@+=*$!&+6!3*&$@1*$!&)%@2!89!
(+=.*$!41%3!.*&6!2%!.**#:
!
B.*!#&1Q+\!%1!'%(=*!)%\!3%'*$!(+!&!
K&Q!$(3(#&1!2%!3%'*3*+2!$**+!6@1(+L!
=1Q(+L!&42*1!)(12.:!
!
B.*!$>(+!.&$!6*'*#%-*6!$K*&2!L#&+6$!&+6!($!=%'*1*6!)Q!&!L1*&$Q!K.(2*!$@)$2&+=*!
6%=2%1$!=&##!M'*1+(\?P!K.(=.!-1%2*=2$!2.*!$>(+!41%3!2.*!#%+L!*\-%$@1*!2%!&3+(%2(=!
4#@(6:!
!
"2!A8!K**>$!)1*&2.(+L!-&22*1+$?!)%6Q!3%'*3*+2$!&+6!.*&12!1&2*!)*L(+!2%!4%##%K!
6&(#Q!=Q=#*$!=&##*6!=(1=&6(&+!1.Q2.3$:!!
22 to 24 Weeks!
RQ!AA!K**>$!.*&1(+L!&+6!1*$-%+$*!2%!
'&1(%@$!$%@+6$!)*L(+!&$!2.*!=%=.#*&?!
2.*!%1L&+!%4!.*&1(+L?!1*&=.*$!&6@#2!
$(c*:!"##!$>(+!#&Q*1$!&+6!$21@=2@1*$!&1*!
=%3-#*2*:!
B.*!@+)%1+!=.(#6!1*&=2$!2%!$2(3@#(!2.&2!
K%@#6!)*!1*=%L+(c*6!&$!-&(+4@#!(4!
&--#(*6!2%!&+!&6@#2!.@3&+:!
!
B.*!AADK**>!@+)%1+!=.(#6!K*(L.$!W@$2!#*$$!2.&+!8!-%@+6!&+6!3*&$@1*$!&)%@2!88!
)
(+=.*$!41%3!.*&6!2%!.**#:!
;(2.!$-*=(&#(c*6!3*6(=&#!=&1*!$%3*!(+4&+2$!)%1+!)Q!AA!K**>$!=&+!#('*!%@2$(6*!2.*!
K%3)!K(2.!$@1'('&#!1&2*$!1*-%12*6!&$!.(L.!&$!F9i!(+!$%3*!3*6(=&#!=*+2*1$:!
R*2K**+!A9!&+6!Ae!K**>$ 1&-(6!*Q*!3%'*3*+2$!)*L(+?!K.(=.!&1*!$(3(#&1!2%!2.*!
MO7]!$#**-P!-&22*1+!$**+!K.*+!=.(#61*+!&+6!&6@#2$!.&'*!61*&3$:!
24 to 26 Weeks!
!
"2!AF!K**>$?!2.*!@+)%1+!=.(#6!($!&)%@2!
8A!(+=.*$!41%3!.*&6!2%!.**#!&+6!
K*(L.$!&)%@2!8g!-%@+6$:!
,@1'('&#!1&2*$!4%1!(+4&+2$!)%1+!&2!AF!
K**>$!&1*!1*-%12*6!&$!.(L.!&$!H8!
-*1=*+2:!
RQ!AF!K**>$!3%1*!2.&+!e9!3(##(%+!
.*&12)*&2$!.&'*!)**+!-*14%13*6:!
RQ!AI!K**>$?!)1*&2.(+L!3%2(%+$!3&Q!%==@1!@-!2%!FF!2(3*$!-*1!3(+@2*:!
26 to 28 Weeks!
B.*!ACDK**>!@+)%1+!=.(#6!K*(L.$!&#3%$2!
A!-%@+6$!&+6!3*&$@1*$!&)%@2!8F!(+=.*$!
41%3!.*&6!2%!.**#:!
RQ!AC!K**>$!$@66*+?!#%@6!+%($*$!21(LL*1!
&!)#(+>D$2&12#*!1*$-%+$*!&+6!3&Q!(+=1*&$*!
3%'*3*+2?!.*&12!1&2*?!&+6!$K&##%K(+L:!
B.*!#@+L$!-1%6@=*!&!$@)$2&+=*!+*=*$$&1Q!
!*
4%1!)1*&2.(+L!&42*1!)(12.:!
B.*!$@1'('&#!1&2*!%4!(+4&+2$!)%1+!&2!AC!K**>$!($!1*-%12*6!&$!.(L.!&$![I!-*1=*+2:!
RQ!AE!K**>$!2.*!2.(L.!)%+*!&+6!2.*!4%%2!)%+*$!&1*!*&=.!&)%@2!2K%!(+=.*$!#%+L!
T&)%@2!I!=3U:!!
28 to 30 Weeks!
RQ!AH!K**>$!2.*!$*+$*!%4!$3*##!($!
4@+=2(%+(+L!&+6!*Q*$!-1%6@=*!2*&1$:!!
B.*!AHDK**>!@+)%1+!=.(#6!K*(L.$!3%1*!
2.&+!Ah!-%@+6$!&+6!3*&$@1*$!&)%@2!8I!
(+=.*$!41%3!.*&6!2%!.**#:!
Nearly all infants born between this
point and full term survive.
RQ!A[!K**>$?!-@-(#$!%4!2.*!*Q*$!1*&=2!2%!#(L.2:!!
30 to 32 Weeks!
"2!e9!K**>$?!2.*!@+)%1+!=.(#6!K*(L.$!
&)%@2!eg!-%@+6$!&+6!3*&$@1*$!&)%@2!
8C!(+=.*$!41%3!.*&6!2%!.**#:!
RQ!e8!K**>$!2.*!.*&12!.&$!)*&2!3%1*!
2.&+!F9!3(##(%+!2(3*$:!
;1(+>#*$!(+!2.*!$>(+!&1*!6($&--*&1(+L!
&$!3%1*!&+6!3%1*!4&2!6*-%$(2$!&1*!
4%13*6:!
!!
32 to 34 Weeks!
!
RQ!eA!K**>$!)1*&2.(+L!3%'*3*+2$!
%==@1!@-!2%!F9!-*1=*+2!%4!2.*!2(3*:!!
B.*!eADK**>!@+)%1+!=.(#6!K*(L.$!&)%@2!
F!-%@+6$!&+6!3*&$@1*$!&)%@2!8E!(+=.*$!
41%3!.*&6!2%!.**#:!
34 to 36 Weeks!
RQ!eF!K**>$!21@*!&#'*%#(!T&#D' j!D#"U?!%1!
&(1!k-%=>*2k!=*##$?!)*L(+!6*'*#%-(+L!(+!
2.*!#@+L$:!
B.*!eFDK**>!@+)%1+!=.(#6!K*(L.$!
&)%@2!I!-%@+6$!&+6!3*&$@1*$!&)%@2!8H!
(+=.*$!41%3!.*&6!2%!.**#:!
!
!"
36 to 38 Weeks!
"2!eC!K**>$?!2.*!@+)%1+!=.(#6!K*(L.$!
&)%@2!Il!-%@+6$!&+6!3*&$@1*$!&)%@2!
8Hh!(+=.*$!41%3!.*&6!2%!.**#:!
,=&#-!.&(1!($!$(#>Q!&+6!#(*$!&L&(+$2!2.*!
.*&6:!
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