The Saatchi & Saatchi Italy-created video starts with on-screen text that summarises a letter sent to the organisation by an expectant mother who has just found out her unborn child has Downs Syndrome.
During the video, people with the syndrome reassure the mother, before their own mothers appear alongside them.
The most-shared ad for a second week in a row was Wren Clothing's "first kiss". The ad, which was shared 275,594 times this week, was created and directed by Tatia Pilieva and features pairs of strangers kissing for the first time.
Elsewhere in the chart, a teaser for an upcoming campaign for Adidas-brand Neo starring Justin Bieber appeared in sixth place.
The ad, shared 40,065 times this week, is silent and stars Bieber dancing around a microphone stand.
1. Wren Clothing "first kiss" by Tatia Pilieva
275,594 shares this week | 1,364,999 shares all-time
2. Coordown "dear future mom" by Saatchi & Saatchi, Italy
225,500 shares this week | 186,398 shares all-time
3. Samsung "samsung galaxy s5 : official hands-on" created in-house
170,695 shares this week | 193,558 shares all-time
4. Samsung "samsung gear fit : official hands-on" created in-house
63,663 shares this week | 80,618 shares all-time
5. Save the Children "most shocking second a day video" by Don't Panic London
55,400 shares this week | 845,895 shares all-time
6. Adidas "#neobiebermix teaser"
40,065 shares this week | 37,133 shares all-time
7. Google "android wear: information that moves with you"
26,270 shares this week | 26,270 shares all-time
8. Mayhew Animal Home "unloved" by BBH London
24,486 shares this week | 81,944 shares all-time
9. Duracell Canada"moments of warmth" by
19,181 shares this week | 29,339 shares all-time
10. Edeka "supergeil" by Jung Von Matt
18,781 shares this week | 385,374 shares all-time